1 files changed, 1 insertions, 0 deletions
diff --git a/src/wasm-builder.h b/src/wasm-builder.h
index 02304acec..b8de8ce25 100644
--- a/src/wasm-builder.h
+++ b/src/wasm-builder.h
@@ -375,6 +375,7 @@ public:
 
   static Index addVar(Function* func, Name name, Type type) {
     // always ok to add a var, it does not affect other indices
+    assert(isConcreteType(type));
     Index index = func->getNumLocals();
     if (name.is()) {
       func->localIndices[name] = index;