diff --git a/library/gcm.c b/library/gcm.c
index 77b1e0f..2456c40 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -354,7 +354,7 @@
     /* Total length is restricted to 2^39 - 256 bits, ie 2^36 - 2^5 bytes
      * Also check for possible overflow */
     if( ctx->len + length < ctx->len ||
-        (uint64_t) ctx->len + length > 0x03FFFFE0llu )
+        (uint64_t) ctx->len + length > 0x03FFFFE0ull )
     {
         return( POLARSSL_ERR_GCM_BAD_INPUT );
     }