diff --git a/lib/jasmine-core/jasmine.js b/lib/jasmine-core/jasmine.js
index f0a41428..6e6d4d59 100644
--- a/lib/jasmine-core/jasmine.js
+++ b/lib/jasmine-core/jasmine.js
@@ -1056,6 +1056,9 @@ getJasmineRequireObj().Clock = function() {
 
 
     self.install = function() {
+      if(!originalTimingFunctionsIntact()) {
+        throw new Error('Jasmine Clock was unable to install over custom global timer functions. Is the clock already installed?');
+      }
       replace(global, fakeTimingFunctions);
       timer = fakeTimingFunctions;
       delayedFunctionScheduler = delayedFunctionSchedulerFactory();
@@ -1125,6 +1128,13 @@ getJasmineRequireObj().Clock = function() {
 
     return self;
 
+    function originalTimingFunctionsIntact() {
+      return global.setTimeout === realTimingFunctions.setTimeout &&
+        global.clearTimeout === realTimingFunctions.clearTimeout &&
+        global.setInterval === realTimingFunctions.setInterval &&
+        global.clearInterval === realTimingFunctions.clearInterval;
+    }
+
     function legacyIE() {
       //if these methods are polyfilled, apply will be present
       return !(realTimingFunctions.setTimeout || realTimingFunctions.setInterval).apply;
diff --git a/spec/core/ClockSpec.js b/spec/core/ClockSpec.js
index cda0d448..7ed8264a 100644
--- a/spec/core/ClockSpec.js
+++ b/spec/core/ClockSpec.js
@@ -88,6 +88,78 @@ describe("Clock", function() {
     expect(fakeClearInterval).not.toHaveBeenCalled();
   });
 
+  it("does not install if the current setTimeout is not the original function on the global", function() {
+    var originalFakeSetTimeout = function() {},
+      replacedSetTimeout = function() {},
+      fakeGlobal = { setTimeout: originalFakeSetTimeout },
+      delayedFunctionSchedulerFactory = jasmine.createSpy('delayedFunctionSchedulerFactory'),
+      mockDate = {},
+      clock = new j$.Clock(fakeGlobal, delayedFunctionSchedulerFactory, mockDate);
+
+    fakeGlobal.setTimeout = replacedSetTimeout;
+
+    expect(function() {
+      clock.install();
+    }).toThrowError(/unable to install/);
+
+    expect(delayedFunctionSchedulerFactory).not.toHaveBeenCalled();
+    expect(fakeGlobal.setTimeout).toBe(replacedSetTimeout);
+  });
+
+  it("does not install if the current clearTimeout is not the original function on the global", function() {
+    var originalFakeClearTimeout = function() {},
+      replacedClearTimeout = function() {},
+      fakeGlobal = { clearTimeout: originalFakeClearTimeout },
+      delayedFunctionSchedulerFactory = jasmine.createSpy('delayedFunctionSchedulerFactory'),
+      mockDate = {},
+      clock = new j$.Clock(fakeGlobal, delayedFunctionSchedulerFactory, mockDate);
+
+    fakeGlobal.clearTimeout = replacedClearTimeout;
+
+    expect(function() {
+      clock.install();
+    }).toThrowError(/unable to install/);
+
+    expect(delayedFunctionSchedulerFactory).not.toHaveBeenCalled();
+    expect(fakeGlobal.clearTimeout).toBe(replacedClearTimeout);
+  });
+
+  it("does not install if the current setInterval is not the original function on the global", function() {
+    var originalFakeSetInterval = function() {},
+      replacedSetInterval = function() {},
+      fakeGlobal = { setInterval: originalFakeSetInterval },
+      delayedFunctionSchedulerFactory = jasmine.createSpy('delayedFunctionSchedulerFactory'),
+      mockDate = {},
+      clock = new j$.Clock(fakeGlobal, delayedFunctionSchedulerFactory, mockDate);
+
+    fakeGlobal.setInterval = replacedSetInterval;
+
+    expect(function() {
+      clock.install();
+    }).toThrowError(/unable to install/);
+
+    expect(delayedFunctionSchedulerFactory).not.toHaveBeenCalled();
+    expect(fakeGlobal.setInterval).toBe(replacedSetInterval);
+  });
+
+  it("does not install if the current clearInterval is not the original function on the global", function() {
+    var originalFakeClearInterval = function() {},
+      replacedClearInterval = function() {},
+      fakeGlobal = { clearInterval: originalFakeClearInterval },
+      delayedFunctionSchedulerFactory = jasmine.createSpy('delayedFunctionSchedulerFactory'),
+      mockDate = {},
+      clock = new j$.Clock(fakeGlobal, delayedFunctionSchedulerFactory, mockDate);
+
+    fakeGlobal.clearInterval = replacedClearInterval;
+
+    expect(function() {
+      clock.install();
+    }).toThrowError(/unable to install/);
+
+    expect(delayedFunctionSchedulerFactory).not.toHaveBeenCalled();
+    expect(fakeGlobal.clearInterval).toBe(replacedClearInterval);
+  });
+
   it("replaces the global timer functions on uninstall", function() {
     var fakeSetTimeout = jasmine.createSpy("global setTimeout"),
       fakeClearTimeout = jasmine.createSpy("global clearTimeout"),
diff --git a/src/core/Clock.js b/src/core/Clock.js
index e07e9217..474a4fb7 100644
--- a/src/core/Clock.js
+++ b/src/core/Clock.js
@@ -19,6 +19,9 @@ getJasmineRequireObj().Clock = function() {
 
 
     self.install = function() {
+      if(!originalTimingFunctionsIntact()) {
+        throw new Error('Jasmine Clock was unable to install over custom global timer functions. Is the clock already installed?');
+      }
       replace(global, fakeTimingFunctions);
       timer = fakeTimingFunctions;
       delayedFunctionScheduler = delayedFunctionSchedulerFactory();
@@ -88,6 +91,13 @@ getJasmineRequireObj().Clock = function() {
 
     return self;
 
+    function originalTimingFunctionsIntact() {
+      return global.setTimeout === realTimingFunctions.setTimeout &&
+        global.clearTimeout === realTimingFunctions.clearTimeout &&
+        global.setInterval === realTimingFunctions.setInterval &&
+        global.clearInterval === realTimingFunctions.clearInterval;
+    }
+
     function legacyIE() {
       //if these methods are polyfilled, apply will be present
       return !(realTimingFunctions.setTimeout || realTimingFunctions.setInterval).apply;