diff --git a/spec/suites/MatchersSpec.js b/spec/suites/MatchersSpec.js
index 67295fb..32b7e5f 100644
--- a/spec/suites/MatchersSpec.js
+++ b/spec/suites/MatchersSpec.js
@@ -513,6 +513,22 @@ describe("jasmine.Matchers", function() {
       match(false).not.custom();
       expect(lastResult().message).toEqual("Passed.");
     });
+
+    it("should make old-style custom matchers blow up, but only when negated", function() {
+      spec.addMatchers({
+        custom: function() {
+          this.report();
+        }
+      });
+
+      expect(function() {
+        match(true).custom();
+      }).not.toThrow();
+
+      expect(function() {
+        match(true).not.custom();
+      }).toThrow();
+    });
   });
 
   describe("spy matchers >>", function() {
diff --git a/src/Matchers.js b/src/Matchers.js
index d387d52..4b27692 100644
--- a/src/Matchers.js
+++ b/src/Matchers.js
@@ -18,8 +18,12 @@ jasmine.Matchers.pp = function(str) {
 
 /** @deprecated */
 jasmine.Matchers.prototype.report = function(result, failing_message, details) {
-//  todo first: report deprecation warning [xw]
-//  todo later: throw new Error("As of jasmine 0.xx, custom matchers must be implemented differently -- please see jasmine docs");
+  // todo: report a deprecation warning [xw]
+
+  if (this.isNot) {
+    throw new Error("As of jasmine 0.11, custom matchers must be implemented differently -- please see jasmine docs");
+  }
+  
   this.reportWasCalled_ = true;
   var expectationResult = new jasmine.ExpectationResult({
     passed: result,