diff --git a/lib/compress.js b/lib/compress.js
index cc691c43..11f3311f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -673,6 +673,7 @@ merge(Compressor.prototype, {
                     var lhs = get_lhs(candidate);
                     if (!lhs || is_lhs_read_only(lhs)) continue;
                     var lvalues = get_lvalues(candidate);
+                    if (lhs instanceof AST_SymbolRef) lvalues[lhs.name] = false;
                     var side_effects = value_has_side_effects(candidate);
                     var hit = false, abort = false, replaced = false;
                     var tt = new TreeTransformer(function(node, descend) {
@@ -697,10 +698,10 @@ merge(Compressor.prototype, {
                             return node;
                         }
                         // Replace variable with assignment when found
-                        if (lhs.equivalent_to(node)) {
-                            abort = true;
-                            if (is_lhs(node, parent)) return node;
-                            CHANGED = replaced = true;
+                        if (!(node instanceof AST_SymbolDeclaration)
+                            && !is_lhs(node, parent)
+                            && lhs.equivalent_to(node)) {
+                            CHANGED = replaced = abort = true;
                             compressor.info("Collapsing {name} [{file}:{line},{col}]", {
                                 name: node.print_to_string(),
                                 file: node.start.file,
@@ -723,24 +724,6 @@ merge(Compressor.prototype, {
                             }
                             return candidate;
                         }
-                        if (lhs instanceof AST_SymbolRef) {
-                            // `a = x; a = a + y;` => `a = x + y;`
-                            if (node instanceof AST_Assign
-                                && node.operator == "="
-                                && lhs.equivalent_to(node.left)) {
-                                node.right = node.right.transform(tt);
-                                abort = true;
-                                return node;
-                            }
-                            // `var a = x, a = a + y;` => `var a = x + y;`
-                            if (node instanceof AST_VarDef
-                                && node.value
-                                && node.name.definition() === lhs.definition()) {
-                                node.value = node.value.transform(tt);
-                                abort = true;
-                                return node;
-                            }
-                        }
                         // These node types have child nodes that execute sequentially,
                         // but are otherwise not safe to scan into or beyond them.
                         var sym;
@@ -748,9 +731,9 @@ merge(Compressor.prototype, {
                             || node instanceof AST_Exit
                             || node instanceof AST_PropAccess
                             || node instanceof AST_SymbolRef
-                               && (lvalues && lvalues[node.name]
+                               && (lvalues[node.name]
                                    || side_effects && !references_in_scope(node.definition()))
-                            || lvalues && (sym = lhs_or_def(node)) && get_symbol(sym).name in lvalues
+                            || (sym = lhs_or_def(node)) && get_symbol(sym).name in lvalues
                             || parent instanceof AST_Binary
                                 && (parent.operator == "&&" || parent.operator == "||")
                             || parent instanceof AST_Case
@@ -807,8 +790,9 @@ merge(Compressor.prototype, {
             }
 
             function get_lvalues(expr) {
-                if (expr instanceof AST_Unary) return;
-                var lvalues, scope;
+                var lvalues = Object.create(null);
+                if (expr instanceof AST_Unary) return lvalues;
+                var scope;
                 var tw = new TreeWalker(function(node, descend) {
                     if (node instanceof AST_Scope) {
                         var save_scope = scope;
@@ -819,7 +803,6 @@ merge(Compressor.prototype, {
                     if (node instanceof AST_SymbolRef || node instanceof AST_PropAccess) {
                         var sym = get_symbol(node);
                         if (sym instanceof AST_SymbolRef) {
-                            if (!lvalues) lvalues = Object.create(null);
                             lvalues[sym.name] = lvalues[sym.name] || is_lhs(node, tw.parent());
                         }
                     }