diff --git a/lib/compress.js b/lib/compress.js
index 7d20a4ea..db448563 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -89,13 +89,15 @@ merge(Compressor.prototype, {
     },
     before: function(node, descend, in_list) {
         if (node._squeezed) return node;
-        var was_scope = false;
+        // asm.js: drop unused only, leave everything else as is inside "use asm" scope
+        var asm = this.has_directive("use asm"),
+            was_scope = false;
         if (node instanceof AST_Scope) {
-            node = node.hoist_declarations(this);
+            if (!asm) node = node.hoist_declarations(this);
             was_scope = true;
         }
         descend(node, this);
-        node = node.optimize(this);
+        if (!asm) node = node.optimize(this);
         if (was_scope && node instanceof AST_Scope) {
             node.drop_unused(this);
             descend(node, this);
@@ -893,6 +895,15 @@ merge(Compressor.prototype, {
         def(AST_Constant, function(compressor){ return false });
         def(AST_This, function(compressor){ return false });
 
+        // asm.js: `new stdlib.XYZ` inside "use asm" scope are always pure
+        def(AST_New, function(compressor){
+            if (compressor.has_directive("use asm")) return false;
+            // AST_Call fallback
+            var pure = compressor.option("pure_funcs");
+            if (!pure) return true;
+            return pure.indexOf(this.expression.print_to_string()) < 0;
+        });
+
         def(AST_Call, function(compressor){
             var pure = compressor.option("pure_funcs");
             if (!pure) return true;