diff --git a/lib/scope.js b/lib/scope.js
index 32059c07..fb583291 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -220,7 +220,8 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
                 }
             }
             node.thedef = sym;
-            if (parent instanceof AST_Assign || parent instanceof AST_Unary && (parent.operator === '++' || parent.operator === '--')) {
+            if (parent instanceof AST_Unary && (parent.operator === '++' || parent.operator === '--')
+             || parent instanceof AST_Assign && parent.left === node) {
                 sym.modified = true;
             }
             node.reference();