1 files changed, 6 insertions, 1 deletions
diff --git a/lib/compress.js b/lib/compress.js
index 85bb0910..fe504164 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3279,7 +3279,12 @@ merge(Compressor.prototype, {
         });
         def(AST_Assign, function(compressor){
             var left = this.left;
-            if (left.has_side_effects(compressor)) return this;
+            if (left.has_side_effects(compressor)
+                || compressor.has_directive("use strict")
+                    && left instanceof AST_PropAccess
+                    && left.expression.is_constant()) {
+                return this;
+            }
             this.write_only = true;
             while (left instanceof AST_PropAccess) {
                 left = left.expression;