diff --git a/lib/nodes.js b/lib/nodes.js
index b99fe9ef..59b3e41a 100644
--- a/lib/nodes.js
+++ b/lib/nodes.js
@@ -1476,7 +1476,7 @@
       if (this.isChainable() && this.first.isChainable()) {
         allInvertable = true;
         curr = this;
-        while (curr && (curr.operator != null)) {
+        while (curr && curr.operator) {
           allInvertable && (allInvertable = curr.operator in INVERSIONS);
           curr = curr.first;
         }
@@ -1484,7 +1484,7 @@
           return new Parens(this).invert();
         }
         curr = this;
-        while (curr && (curr.operator != null)) {
+        while (curr && curr.operator) {
           curr.invert = !curr.invert;
           curr.operator = INVERSIONS[curr.operator];
           curr = curr.first;
diff --git a/src/nodes.coffee b/src/nodes.coffee
index 5d340e01..06fb8437 100644
--- a/src/nodes.coffee
+++ b/src/nodes.coffee
@@ -1175,13 +1175,13 @@ exports.Op = class Op extends Base
   invert: ->
     if @isChainable() and @first.isChainable()
       allInvertable = yes
-      curr = @
-      while curr and curr.operator?
-        allInvertable &&= (curr.operator of INVERSIONS)
+      curr = this
+      while curr and curr.operator
+        allInvertable and= (curr.operator of INVERSIONS)
         curr = curr.first
       return new Parens(this).invert() unless allInvertable
-      curr = @
-      while curr and curr.operator?
+      curr = this
+      while curr and curr.operator
         curr.invert = !curr.invert
         curr.operator = INVERSIONS[curr.operator]
         curr = curr.first