diff --git a/wolfcrypt/src/tfm.c b/wolfcrypt/src/tfm.c
index 4098ebfd9..b5d76270a 100644
--- a/wolfcrypt/src/tfm.c
+++ b/wolfcrypt/src/tfm.c
@@ -1027,12 +1027,10 @@ void fp_mod_2d(fp_int *a, int b, fp_int *c)
     c->dp[x] = 0;
   }
   /* clear the digit that is not completely outside/inside the modulus */
-  x = DIGIT_BIT - b;
-  if (x > 0) {
-    c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> x;
+  x = DIGIT_BIT - (b % DIGIT_BIT);
+  if (x != DIGIT_BIT) {
+     c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> x;
   }
-  else
-    c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) << -x;
 
   fp_clamp (c);
 }