diff --git a/lib/fko_hmac.c b/lib/fko_hmac.c
index dac961bd..337a638a 100644
--- a/lib/fko_hmac.c
+++ b/lib/fko_hmac.c
@@ -48,6 +48,9 @@ fko_verify_hmac(fko_ctx_t ctx,
     if(!CTX_INITIALIZED(ctx))
         return(FKO_ERROR_CTX_NOT_INITIALIZED);
 
+    if(hmac_key == NULL)
+        return(FKO_ERROR_INVALID_DATA);
+
     if (! is_valid_encoded_msg_len(ctx->encrypted_msg_len))
         return(FKO_ERROR_INVALID_DATA_HMAC_MSGLEN_VALIDFAIL);
 
@@ -230,6 +233,9 @@ int fko_set_spa_hmac(fko_ctx_t ctx,
     if(!CTX_INITIALIZED(ctx))
         return(FKO_ERROR_CTX_NOT_INITIALIZED);
 
+    if(hmac_key == NULL)
+        return(FKO_ERROR_INVALID_DATA);
+
     if(hmac_key_len < 0 || hmac_key_len > MAX_DIGEST_BLOCK_LEN)
         return(FKO_ERROR_INVALID_HMAC_KEY_LEN);