diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 23077d236a9..d89e1688677 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -5136,8 +5136,8 @@ Name WasmBinaryReader::escape(Name name) {
     }
     // replace non-idchar with `\xx` escape
     escaped.push_back('\\');
-    escaped.push_back(formatNibble(c >> 4));
-    escaped.push_back(formatNibble(c & 15));
+    escaped.push_back(formatNibble((unsigned char)c >> 4));
+    escaped.push_back(formatNibble((unsigned char)c & 15));
   }
   return escaped;
 }