diff --git a/wolfcrypt/src/sp_int.c b/wolfcrypt/src/sp_int.c
index 952712fa0..072801135 100644
--- a/wolfcrypt/src/sp_int.c
+++ b/wolfcrypt/src/sp_int.c
@@ -442,13 +442,16 @@ int sp_to_unsigned_bin_len(sp_int* a, byte* out, int outSz)
     int i, j, b;
 
     j = outSz - 1;
-    for (i=0; j>=0; i++) {
+    for (i = 0; j >= 0 && i < a->used; i++) {
         for (b = 0; b < SP_WORD_SIZE; b += 8) {
             out[j--] = a->dp[i] >> b;
             if (j < 0)
                 break;
         }
     }
+    for (; j >= 0; j--) {
+        out[j] = 0;
+    }
 
     return MP_OKAY;
 }
diff --git a/wolfcrypt/src/tfm.c b/wolfcrypt/src/tfm.c
index bf128174e..35d4f806d 100644
--- a/wolfcrypt/src/tfm.c
+++ b/wolfcrypt/src/tfm.c
@@ -3645,12 +3645,15 @@ int fp_to_unsigned_bin_len(fp_int *a, unsigned char *b, int c)
 #if DIGIT_BIT == 64 || DIGIT_BIT == 32
   int i, j, x;
 
-  for (x=c-1,j=0,i=0; x >= 0; x--) {
+  for (x=c-1, j=0, i=0; x >= 0 && i < a->used; x--) {
      b[x] = (unsigned char)(a->dp[i] >> j);
      j += 8;
      i += j == DIGIT_BIT;
      j &= DIGIT_BIT - 1;
   }
+  for (; x >= 0; x--) {
+     b[x] = 0;
+  }
 
   return FP_OKAY;
 #else