diff --git a/crypto/fipsmodule/bn/exponentiation.cc.inc b/crypto/fipsmodule/bn/exponentiation.cc.inc
index a6c7d55..e537476 100644
--- a/crypto/fipsmodule/bn/exponentiation.cc.inc
+++ b/crypto/fipsmodule/bn/exponentiation.cc.inc
@@ -343,7 +343,7 @@
 
 void bn_mod_inverse0_prime_mont_small(BN_ULONG *r, const BN_ULONG *a,
                                       size_t num, const BN_MONT_CTX *mont) {
-  if (num != (size_t)mont->N.width || num > BN_SMALL_MAX_WORDS) {
+  if (num != (size_t)mont->N.width || num > BN_SMALL_MAX_WORDS || num == 0) {
     abort();
   }