diff --git a/crypto/hmac/hmac.c b/crypto/hmac/hmac.c
index b1aa05b2e..16d95e08d 100644
--- a/crypto/hmac/hmac.c
+++ b/crypto/hmac/hmac.c
@@ -89,7 +89,7 @@ void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int len,
 			}
 		else
 			{
-			OPENSSL_assert(len>0 && len <= (int)sizeof(ctx->key));
+			OPENSSL_assert(len>=0 && len<=(int)sizeof(ctx->key));
 			memcpy(ctx->key,key,len);
 			ctx->key_length=len;
 			}