1 files changed, 1 insertions, 1 deletions
diff --git a/lib/compress.js b/lib/compress.js
index 7bbb5a20..09d416cf 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3856,7 +3856,7 @@ merge(Compressor.prototype, {
             if (!(rhs instanceof AST_Binary && lazy_op[rhs.operator])) return rhs;
             var sym = assign.left;
             if (!(sym instanceof AST_SymbolRef) || sym.name != rhs.left.name) return rhs;
-            return rhs.right;
+            return rhs.right.has_side_effects(compressor) ? rhs : rhs.right;
         }
 
         function scan_ref_scoped(node, descend) {