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diff --git a/tools/eslint/lib/rules/no-negated-in-lhs.js b/tools/eslint/lib/rules/no-negated-in-lhs.js
new file mode 100644
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+++ b/tools/eslint/lib/rules/no-negated-in-lhs.js
@@ -0,0 +1,23 @@
+/**
+ * @fileoverview A rule to disallow negated left operands of the `in` operator
+ * @author Michael Ficarra
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    return {
+
+        "BinaryExpression": function(node) {
+            if (node.operator === "in" && node.left.type === "UnaryExpression" && node.left.operator === "!") {
+                context.report(node, "The `in` expression's left operand is negated");
+            }
+        }
+    };
+
+};