diff --git a/lib/compress.js b/lib/compress.js
index 81d84906..656ef757 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1167,12 +1167,36 @@ merge(Compressor.prototype, {
     }
 
     (function(def) {
-        def(AST_Node, return_false);
+        def(AST_Node, return_true);
         def(AST_Null, return_true);
         def(AST_Undefined, return_true);
+        def(AST_Constant, return_false);
+        def(AST_Array, return_false);
+        def(AST_Object, return_false);
+        def(AST_Function, return_false);
+        def(AST_UnaryPostfix, return_false);
         def(AST_UnaryPrefix, function() {
             return this.operator == "void";
         });
+        def(AST_Binary, function(compressor) {
+            switch (this.operator) {
+              case "&&":
+                return this.left.may_eq_null(compressor);
+              case "||":
+                return this.left.may_eq_null(compressor)
+                    && this.right.may_eq_null(compressor);
+              default:
+                return false;
+            }
+        })
+        def(AST_Assign, function(compressor) {
+            return this.operator == "="
+                && this.right.may_eq_null(compressor);
+        })
+        def(AST_Conditional, function(compressor) {
+            return this.consequent.may_eq_null(compressor)
+                || this.alternative.may_eq_null(compressor);
+        })
         def(AST_Seq, function(compressor) {
             return this.cdr.may_eq_null(compressor);
         });