diff --git a/datCrawl/__init__.py b/datCrawl/__init__.py
index 38736bb..5084af7 100644
--- a/datCrawl/__init__.py
+++ b/datCrawl/__init__.py
@@ -1,6 +1,6 @@
 from datCrawl.exceptions import CrawlerDontHaveUrlsToWatch, \
     CrawlerIsNotInstanceOfBaseCrawler, CrawlerForThisURLNotFound, \
-    NoCrawlerRegistered
+    NoCrawlerRegistered, CrawlerAlreadyRegistered
 from datCrawl.crawlers import Crawler
 import re
 
@@ -15,15 +15,18 @@ def __init__(self):
     def register_crawler(self, crawler):
         "Registers a crawler on the core to use in certain urls."
         class_name = crawler().__class__.__name__
-        if isinstance(crawler(), Crawler):
-            urls = crawler().urls
-            if len(urls) > 0:
-                [self.register_url(url, action, class_name) for action, url in urls]
-                self.crawlers[class_name] = crawler
+        if class_name not in self.crawlers:
+            if isinstance(crawler(), Crawler):
+                urls = crawler().urls
+                if len(urls) > 0:
+                    [self.register_url(url, action, class_name) for action, url in urls]
+                    self.crawlers[class_name] = crawler
+                else:
+                    raise CrawlerDontHaveUrlsToWatch('Crawler %s dont have URLs to watch for.' % class_name)
             else:
-                raise CrawlerDontHaveUrlsToWatch('Crawler %s dont have URLs to watch for.' % class_name)
+                raise CrawlerIsNotInstanceOfBaseCrawler('Crawler %s is not correctly created. (must be instance of base Crawler class)' % class_name)
         else:
-            raise CrawlerIsNotInstanceOfBaseCrawler('Crawler %s is not correctly created. (must be instance of base Crawler class)' % class_name)
+            raise CrawlerAlreadyRegistered("Crawler %s is already registered." % class_name)
 
     def register_url(self, url, action, crawler):
         "Registers a certain URL to work with a crawler"
diff --git a/datCrawl/exceptions.py b/datCrawl/exceptions.py
index d6b7ee2..1821fcc 100644
--- a/datCrawl/exceptions.py
+++ b/datCrawl/exceptions.py
@@ -21,3 +21,8 @@ class CrawlerActionDoesNotExist(Exception):
 class CrawlerForThisURLNotFound(Exception):
     "When there's no crawler found for a specific URL"
     pass
+
+
+class CrawlerAlreadyRegistered(Exception):
+    "When you try to register the same crawler."
+    pass
diff --git a/test/test_base.py b/test/test_base.py
index c607cdb..790ce62 100644
--- a/test/test_base.py
+++ b/test/test_base.py
@@ -35,6 +35,11 @@ def test_register_urls(self):
         core.register_url(data[0], data[1], data[2])
         self.assertEquals(core.urls[0], data)
 
+    def test_cant_register_crawler_twice(self):
+        core = datCrawl()
+        core.register_crawler(AwesomeGoogleCrawler)
+        self.assertRaises(CrawlerAlreadyRegistered, lambda: core.register_crawler(AwesomeGoogleCrawler))
+
     def test_register_crawler_with_urls(self):
         core = datCrawl()
         core.register_crawler(AwesomeGoogleCrawler)