diff --git a/wolfcrypt/src/sp_arm32.c b/wolfcrypt/src/sp_arm32.c
index 11f187160..13fe73a0f 100644
--- a/wolfcrypt/src/sp_arm32.c
+++ b/wolfcrypt/src/sp_arm32.c
@@ -75856,15 +75856,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_8(r);
 
-            sp_256_from_mp(x, 8, priv);
-            sp_256_from_bin(e, 8, hash, (int)hashLen);
+            if (sp_256_iszero_8(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 8, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 8, hash, (int)hashLen);
 
-            err = sp_256_calc_s_8(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_8(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -93466,15 +93470,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_12(r);
 
-            sp_384_from_mp(x, 12, priv);
-            sp_384_from_bin(e, 12, hash, (int)hashLen);
+            if (sp_384_iszero_12(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 12, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 12, hash, (int)hashLen);
 
-            err = sp_384_calc_s_12(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_12(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -121604,19 +121612,24 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_17(r);
 
-            sp_521_from_mp(x, 17, priv);
-            sp_521_from_bin(e, 17, hash, (int)hashLen);
+            if (sp_521_iszero_17(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 17, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 17, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_17(e, e, 7);
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_17(e, e, 7);
+                }
+
+                err = sp_521_calc_s_17(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_17(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_arm64.c b/wolfcrypt/src/sp_arm64.c
index c61a29e18..97d121d49 100644
--- a/wolfcrypt/src/sp_arm64.c
+++ b/wolfcrypt/src/sp_arm64.c
@@ -40604,15 +40604,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_4(r);
 
-            sp_256_from_mp(x, 4, priv);
-            sp_256_from_bin(e, 4, hash, (int)hashLen);
+            if (sp_256_iszero_4(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 4, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 4, hash, (int)hashLen);
 
-            err = sp_256_calc_s_4(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_4(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_4(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_4(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -66724,15 +66728,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_6(r);
 
-            sp_384_from_mp(x, 6, priv);
-            sp_384_from_bin(e, 6, hash, (int)hashLen);
+            if (sp_384_iszero_6(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 6, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 6, hash, (int)hashLen);
 
-            err = sp_384_calc_s_6(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_6(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_6(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_6(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -111542,19 +111550,24 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_9(r);
 
-            sp_521_from_mp(x, 9, priv);
-            sp_521_from_bin(e, 9, hash, (int)hashLen);
+            if (sp_521_iszero_9(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 9, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 9, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_9(e, e, 7);
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_9(e, e, 7);
+                }
+
+                err = sp_521_calc_s_9(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_9(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_armthumb.c b/wolfcrypt/src/sp_armthumb.c
index ad9f4f4af..6395b7845 100644
--- a/wolfcrypt/src/sp_armthumb.c
+++ b/wolfcrypt/src/sp_armthumb.c
@@ -105816,15 +105816,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_8(r);
 
-            sp_256_from_mp(x, 8, priv);
-            sp_256_from_bin(e, 8, hash, (int)hashLen);
+            if (sp_256_iszero_8(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 8, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 8, hash, (int)hashLen);
 
-            err = sp_256_calc_s_8(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_8(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -116585,15 +116589,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_12(r);
 
-            sp_384_from_mp(x, 12, priv);
-            sp_384_from_bin(e, 12, hash, (int)hashLen);
+            if (sp_384_iszero_12(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 12, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 12, hash, (int)hashLen);
 
-            err = sp_384_calc_s_12(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_12(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -132784,19 +132792,24 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_17(r);
 
-            sp_521_from_mp(x, 17, priv);
-            sp_521_from_bin(e, 17, hash, (int)hashLen);
+            if (sp_521_iszero_17(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 17, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 17, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_17(e, e, 7);
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_17(e, e, 7);
+                }
+
+                err = sp_521_calc_s_17(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_17(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_c32.c b/wolfcrypt/src/sp_c32.c
index 5baa62eee..74b050105 100644
--- a/wolfcrypt/src/sp_c32.c
+++ b/wolfcrypt/src/sp_c32.c
@@ -25796,15 +25796,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_9(r);
 
-            sp_256_from_mp(x, 9, priv);
-            sp_256_from_bin(e, 9, hash, (int)hashLen);
+            if (sp_256_iszero_9(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 9, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 9, hash, (int)hashLen);
 
-            err = sp_256_calc_s_9(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_9(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_9(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_9(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -33873,15 +33877,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_15(r);
 
-            sp_384_from_mp(x, 15, priv);
-            sp_384_from_bin(e, 15, hash, (int)hashLen);
+            if (sp_384_iszero_15(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 15, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 15, hash, (int)hashLen);
 
-            err = sp_384_calc_s_15(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_15(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_15(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_15(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -42024,20 +42032,25 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_21(r);
 
-            sp_521_from_mp(x, 21, priv);
-            sp_521_from_bin(e, 21, hash, (int)hashLen);
+            if (sp_521_iszero_21(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 21, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 21, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_21(e, e, 7);
-                e[20] |= ((sp_digit)hash[0]) << 13;
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_21(e, e, 7);
+                    e[20] |= ((sp_digit)hash[0]) << 13;
+                }
+
+                err = sp_521_calc_s_21(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_21(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_21(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_21(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_c64.c b/wolfcrypt/src/sp_c64.c
index bd3b62260..21f265395 100644
--- a/wolfcrypt/src/sp_c64.c
+++ b/wolfcrypt/src/sp_c64.c
@@ -26689,15 +26689,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_5(r);
 
-            sp_256_from_mp(x, 5, priv);
-            sp_256_from_bin(e, 5, hash, (int)hashLen);
+            if (sp_256_iszero_5(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 5, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 5, hash, (int)hashLen);
 
-            err = sp_256_calc_s_5(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_5(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_5(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_5(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -34157,15 +34161,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_7(r);
 
-            sp_384_from_mp(x, 7, priv);
-            sp_384_from_bin(e, 7, hash, (int)hashLen);
+            if (sp_384_iszero_7(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 7, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 7, hash, (int)hashLen);
 
-            err = sp_384_calc_s_7(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_7(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_7(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_7(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -41622,20 +41630,25 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_9(r);
 
-            sp_521_from_mp(x, 9, priv);
-            sp_521_from_bin(e, 9, hash, (int)hashLen);
+            if (sp_521_iszero_9(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 9, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 9, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_9(e, e, 7);
-                e[8] |= ((sp_digit)hash[0]) << 49;
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_9(e, e, 7);
+                    e[8] |= ((sp_digit)hash[0]) << 49;
+                }
+
+                err = sp_521_calc_s_9(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_9(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_cortexm.c b/wolfcrypt/src/sp_cortexm.c
index 9f4007a7f..99c6cc641 100644
--- a/wolfcrypt/src/sp_cortexm.c
+++ b/wolfcrypt/src/sp_cortexm.c
@@ -23710,15 +23710,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_8(r);
 
-            sp_256_from_mp(x, 8, priv);
-            sp_256_from_bin(e, 8, hash, (int)hashLen);
+            if (sp_256_iszero_8(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 8, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 8, hash, (int)hashLen);
 
-            err = sp_256_calc_s_8(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_8(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_8(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -31035,15 +31039,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_12(r);
 
-            sp_384_from_mp(x, 12, priv);
-            sp_384_from_bin(e, 12, hash, (int)hashLen);
+            if (sp_384_iszero_12(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 12, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 12, hash, (int)hashLen);
 
-            err = sp_384_calc_s_12(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_12(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_12(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -39987,19 +39995,24 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_17(r);
 
-            sp_521_from_mp(x, 17, priv);
-            sp_521_from_bin(e, 17, hash, (int)hashLen);
+            if (sp_521_iszero_17(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 17, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 17, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_17(e, e, 7);
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_17(e, e, 7);
+                }
+
+                err = sp_521_calc_s_17(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_17(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_17(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
diff --git a/wolfcrypt/src/sp_x86_64.c b/wolfcrypt/src/sp_x86_64.c
index dbac03baf..d77494169 100644
--- a/wolfcrypt/src/sp_x86_64.c
+++ b/wolfcrypt/src/sp_x86_64.c
@@ -25767,15 +25767,19 @@ int sp_ecc_sign_256(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_256_norm_4(r);
 
-            sp_256_from_mp(x, 4, priv);
-            sp_256_from_bin(e, 4, hash, (int)hashLen);
+            if (sp_256_iszero_4(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_256_from_mp(x, 4, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_256_from_bin(e, 4, hash, (int)hashLen);
 
-            err = sp_256_calc_s_4(s, r, k, x, e, tmp);
-        }
+                err = sp_256_calc_s_4(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_256_iszero_4(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_256_iszero_4(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -50660,15 +50664,19 @@ int sp_ecc_sign_384(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_384_norm_6(r);
 
-            sp_384_from_mp(x, 6, priv);
-            sp_384_from_bin(e, 6, hash, (int)hashLen);
+            if (sp_384_iszero_6(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_384_from_mp(x, 6, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_384_from_bin(e, 6, hash, (int)hashLen);
 
-            err = sp_384_calc_s_6(s, r, k, x, e, tmp);
-        }
+                err = sp_384_calc_s_6(s, r, k, x, e, tmp);
 
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_384_iszero_6(s) == 0)) {
-            break;
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_384_iszero_6(s) == 0)) {
+                    break;
+                }
+            }
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;
@@ -91792,19 +91800,24 @@ int sp_ecc_sign_521(const byte* hash, word32 hashLen, WC_RNG* rng,
                 (sp_digit)0 - (sp_digit)(c >= 0));
             sp_521_norm_9(r);
 
-            sp_521_from_mp(x, 9, priv);
-            sp_521_from_bin(e, 9, hash, (int)hashLen);
+            if (sp_521_iszero_9(r) == 0) {
+                /* x is modified in calculation of s. */
+                sp_521_from_mp(x, 9, priv);
+                /* s ptr == e ptr, e is modified in calculation of s. */
+                sp_521_from_bin(e, 9, hash, (int)hashLen);
 
-            if (hashLen == 66U) {
-                sp_521_rshift_9(e, e, 7);
+                /* Take 521 leftmost bits of hash. */
+                if (hashLen == 66U) {
+                    sp_521_rshift_9(e, e, 7);
+                }
+
+                err = sp_521_calc_s_9(s, r, k, x, e, tmp);
+
+                /* Check that signature is usable. */
+                if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
+                    break;
+                }
             }
-
-            err = sp_521_calc_s_9(s, r, k, x, e, tmp);
-        }
-
-        /* Check that signature is usable. */
-        if ((err == MP_OKAY) && (sp_521_iszero_9(s) == 0)) {
-            break;
         }
 #ifdef WOLFSSL_ECDSA_SET_K_ONE_LOOP
         i = 1;