diff --git a/asm.js b/asm.js
index 4b89ace..cb1de69 100644
--- a/asm.js
+++ b/asm.js
@@ -752,8 +752,8 @@ export class Assembler {
 
     lookup_local(func, symbol) {
         const param_count = Object.entries(func.params).length;
-        const index = param_count + Object.keys(func.locals).indexOf(symbol);
-        return index == -1 ? null : index;
+        const index = Object.keys(func.locals).indexOf(symbol);
+        return index == -1 ? null : param_count + index;
     }
 
     lookup_global(symbol) {