diff --git a/wolfssl/wolfcrypt/ecc.h b/wolfssl/wolfcrypt/ecc.h
index 94530b2da..3e1a19f80 100644
--- a/wolfssl/wolfcrypt/ecc.h
+++ b/wolfssl/wolfcrypt/ecc.h
@@ -322,7 +322,8 @@ typedef struct ecc_set_type {
 #endif
 
 /* determine buffer size */
-#define FP_SIZE_ECC    (FP_MAX_BITS_ECC/DIGIT_BIT)
+/* Add one to accommodate extra digit used by sp_mul(), sp_mulmod(), sp_sqr(), and sp_sqrmod(). */
+#define FP_SIZE_ECC    ((FP_MAX_BITS_ECC/DIGIT_BIT) + 1)
 
 
 /* This needs to match the size of the fp_int struct, except the
diff --git a/wolfssl/wolfcrypt/sp_int.h b/wolfssl/wolfcrypt/sp_int.h
index 34f88ed8d..431834eb2 100644
--- a/wolfssl/wolfcrypt/sp_int.h
+++ b/wolfssl/wolfcrypt/sp_int.h
@@ -319,9 +319,10 @@ typedef struct sp_ecc_ctx {
     /* Calculate number of digits to have in an sp_int based maximum size of
      * numbers in bits that will be used.
      * Double the size to hold multiplication result.
+     * Add one to accommodate extra digit used by sp_mul(), sp_mulmod(), sp_sqr(), and sp_sqrmod().
      */
     #define SP_INT_DIGITS                                                      \
-        (((SP_INT_BITS + (SP_WORD_SIZE - 1)) * 2 + SP_WORD_SIZE) / SP_WORD_SIZE)
+        ((((SP_INT_BITS + (SP_WORD_SIZE - 1)) * 2 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
 #endif
 
 #ifndef SP_INT_DIGITS
@@ -331,41 +332,41 @@ typedef struct sp_ecc_ctx {
     #if !defined(WOLFSSL_HAVE_SP_RSA) && !defined(WOLFSSL_HAVE_SP_DH) && \
         !defined(WOLFSSL_HAVE_SP_ECC)
         #if !defined(NO_RSA) || !defined(NO_DH) || !defined(NO_DSA)
-            #define SP_INT_DIGITS        ((6144 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((6144 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #elif defined(HAVE_ECC)
             #define SP_INT_DIGITS   \
-                    ((2 * ( 521 + SP_WORD_SIZE) + SP_WORD_SIZE) / SP_WORD_SIZE)
+                    (((2 * ( 521 + SP_WORD_SIZE) + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #elif !defined(NO_PWDBASED) && defined(WOLFSSL_SHA512)
-            #define SP_INT_DIGITS        (( 512 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        ((( 512 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #else
-            #define SP_INT_DIGITS        (( 256 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        ((( 256 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #endif
     #elif !defined(WOLFSSL_HAVE_SP_RSA) && !defined(WOLFSSL_HAVE_SP_DH)
         #ifdef WOLFSSL_SP_MATH_ALL
             #define SP_INT_DIGITS   \
-                    ((2 * ( 521 + SP_WORD_SIZE) + SP_WORD_SIZE) / SP_WORD_SIZE)
+                    (((2 * ( 521 + SP_WORD_SIZE) + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #elif defined(WOLFSSL_SP_384)
-            #define SP_INT_DIGITS        (( 768 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        ((( 768 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #else
-            #define SP_INT_DIGITS        (( 512 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        ((( 512 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #endif
     #elif defined(WOLFSSL_SP_4096)
         #if defined(WOLFSSL_HAVE_SP_DH)
-            #define SP_INT_DIGITS        ((8192 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((8192 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #else
-            #define SP_INT_DIGITS        ((4096 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((4096 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #endif
     #elif !defined(WOLFSSL_SP_NO_3072)
         #if defined(WOLFSSL_HAVE_SP_DH)
-            #define SP_INT_DIGITS        ((6144 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((6144 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #else
-            #define SP_INT_DIGITS        ((3072 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((3072 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #endif
     #else
         #if defined(WOLFSSL_HAVE_SP_DH)
-            #define SP_INT_DIGITS        ((4096 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((4096 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #else
-            #define SP_INT_DIGITS        ((2048 + SP_WORD_SIZE) / SP_WORD_SIZE)
+            #define SP_INT_DIGITS        (((2048 + SP_WORD_SIZE) / SP_WORD_SIZE) + 1)
         #endif
     #endif
 #endif