diff --git a/src/serialize.h b/src/serialize.h
index 7f8f9332843..68501facf20 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -245,7 +245,7 @@ uint64_t ReadCompactSize(Stream& is)
         uint64_t xSize;
         READDATA(is, xSize);
         nSizeRet = xSize;
-        if (nSizeRet < 0x100000000LLu)
+        if (nSizeRet < 0x100000000ULL)
             throw std::ios_base::failure("non-canonical ReadCompactSize()");
     }
     if (nSizeRet > (uint64_t)MAX_SIZE)