diff --git a/wolfcrypt/src/hmac.c b/wolfcrypt/src/hmac.c
index bcebc1ce2..a212dc141 100644
--- a/wolfcrypt/src/hmac.c
+++ b/wolfcrypt/src/hmac.c
@@ -1215,11 +1215,18 @@ int wolfSSL_GetHmacMaxSize(void)
         word32 outIdx = 0;
         word32 hashSz = wc_HmacSizeByType(type);
         byte   n = 0x1;
+        word32 N = 0;  /* rf5869: N = ceil(L/HashLen)*/
+
+        N = (outSz/hashSz) + ((outSz % hashSz) != 0);
+
+        if (out == NULL || N > 255)
+        	return BAD_FUNC_ARG;
 
         ret = wc_HmacInit(&myHmac, NULL, INVALID_DEVID);
         if (ret != 0)
             return ret;
 
+
         while (outIdx < outSz) {
             int    tmpSz = (n == 1) ? 0 : hashSz;
             word32 left = outSz - outIdx;