diff --git a/dom/alarm/AlarmsManager.js b/dom/alarm/AlarmsManager.js
index 9e5ff0becf3f..edefcb01cbdc 100644
--- a/dom/alarm/AlarmsManager.js
+++ b/dom/alarm/AlarmsManager.js
@@ -53,6 +53,10 @@ AlarmsManager.prototype = {
       throw Components.results.NS_ERROR_FAILURE;
     }
 
+    if (!aDate) {
+      throw Components.results.NS_ERROR_INVALID_ARG;
+    }
+
     let isIgnoreTimezone = true;
     switch (aRespectTimezone) {
       case "honorTimezone":
@@ -64,13 +68,13 @@ AlarmsManager.prototype = {
         break;
 
       default:
-        throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+        throw Components.results.NS_ERROR_INVALID_ARG;
         break;
     }
 
     let request = this.createRequest();
     this._cpmm.sendAsyncMessage(
-      "AlarmsManager:Add", 
+      "AlarmsManager:Add",
       { requestId: this.getRequestId(request),
         date: aDate,
         ignoreTimezone: isIgnoreTimezone,
diff --git a/dom/alarm/test/test_alarm_add_date.html b/dom/alarm/test/test_alarm_add_date.html
index 4acb9d85658e..fb724b87c3f7 100644
--- a/dom/alarm/test/test_alarm_add_date.html
+++ b/dom/alarm/test/test_alarm_add_date.html
@@ -25,23 +25,26 @@
     } catch (e) {
       ok(false,
          "Unexpected exception trying to add alarm for tomorrow.");
+
+      // Proceed to next test.
       return testPastDate();
     }
     domRequest.onsuccess = function(e) {
       navigator.mozAlarms.remove(e.target.result);
       ok(true, "Add alarm for future date.");
 
-      // Awesome, no error so proceed to next test
+      // Awesome, no error so proceed to next test.
       testPastDate();
     };
     domRequest.onerror = function(e) {
       ok(false, "Unable to add alarm for tomorrow`.");
+
+      // Proceed to next test.
       testPastDate();
     };
-
   }
 
-  // Verify passing a Date that's already past fails
+  // Verify passing a Date that's already past doesn't fail (it should fire immediately).
   function testPastDate() {
     var yesterday = new Date();
     yesterday.setDate(yesterday.getDate() - 1);
@@ -52,61 +55,61 @@
     } catch (e) {
       ok(false,
          "Unexpected exception trying to add alarm for yesterday.");
-      return testNull();
+
+      // Move on to the next test.
+      testNullDate();
     }
     domRequest.onsuccess = function(e) {
       navigator.mozAlarms.remove(e.target.result);
 
       ok(true, "Should be able to add alarm for already past date, which should fire immediately.");
-      testNull();
+
+      // Move on to the next test.
+      testNullDate();
     };
     domRequest.onerror = function(e) {
       ok(false, "Unable to add alarm for yesterday.");
 
-      // Errors as it should, on to the next test
-      testNull();
+      // Move on to the next test.
+      testNullDate();
     }
   }
 
   // Verify passing null does indeed fail
-  function testNull() {
-    var domRequest;
+  function testNullDate() {
     try {
-      domRequest = navigator.mozAlarms.add(null, "honorTimezone", {});
+      navigator.mozAlarms.add(null, "honorTimezone", {});
+      ok(false, "Expected an exception to be thrown for alarm with null date.");
     } catch(e) {
-      ok(false, "Unexpected exception thrown while testing null case.");
-
-      // Exception thrown
-      return SimpleTest.finish();
+      ok(true, "Exception thrown for alarm with null date.");
     }
-    domRequest.onsuccess = function(e) {
-      // Null should not be valid
-      ok(false, "Null should not be accepted as input for `date` param.");
-      SimpleTest.finish();
-    };
-    domRequest.onerror = function(e) {
-      // Null should not be valid
-      ok(true, "Passing null for date value causes failure.");
 
-      SimpleTest.finish();
-    };
+    // Move on to the next test.
+    testInvalidTimeZone()
+  }
+
+  function testInvalidTimeZone() {
+    try {
+      navigator.mozAlarms.add(new Date(), "badTimeZoneArg", {});
+      ok(false, "Expected an exception to be thrown while testing bad time zone arg.");
+    } catch(e) {
+      ok(true, "Exception thrown while testing bad time zone arg.");
+    }
+    SimpleTest.finish();
   }
 
   function startTests() {
 
     SpecialPowers.pushPrefEnv({"set": [["dom.mozAlarms.enabled", true]]}, function() {
-
       // Currently applicable only on FxOS
       if (navigator.userAgent.indexOf("Mobile") != -1 &&
-          navigator.appVersion.indexOf("Android") == -1) {
-
+          navigator.appVersion.indexOf("Android") == -1)
+      {
         testFutureDate();
-
       } else {
         ok(true, "mozAlarms on Firefox OS only.");
         SimpleTest.finish();
       }
-
     });
   }