diff --git a/third_party/binaryen/BUILD.gn b/third_party/binaryen/BUILD.gn
index d379dd245ee..3adc3c03749 100644
--- a/third_party/binaryen/BUILD.gn
+++ b/third_party/binaryen/BUILD.gn
@@ -18,7 +18,7 @@ config("binaryen_flags") {
   }
 
   # Use legacy encoding for WasmGC instructions
-  cflags += [ "-DUSE_LEGACY_GC_ENCODINGS" ]
+  defines = [ "USE_LEGACY_GC_ENCODINGS" ]
 
   if (is_win) {
     libs = [ "shell32.lib" ]