diff --git a/common/djangoapps/static_replace/__init__.py b/common/djangoapps/static_replace/__init__.py
index 2932c0357a..7167456ed1 100644
--- a/common/djangoapps/static_replace/__init__.py
+++ b/common/djangoapps/static_replace/__init__.py
@@ -48,7 +48,6 @@ def replace_course_urls(text, course_id):
 
 
     def replace_course_url(match):
-        log.warning("Course match: %s", match.groupdict())
         quote = match.group('quote')
         rest = match.group('rest')
         return "".join([quote, '/courses/' + course_id + '/', rest, quote])
@@ -69,31 +68,26 @@ def replace_static_urls(text, data_directory, course_namespace=None):
     """
 
     def replace_static_url(match):
-        log.warning(match.groupdict())
+        original = match.group(0)
         quote = match.group('quote')
         rest = match.group('rest')
 
         # course_namespace is not None, then use studio style urls
         if course_namespace is not None and not isinstance(modulestore(), XMLModuleStore):
             url = StaticContent.convert_legacy_static_url(rest, course_namespace)
-            log.warning("From modulestore: %s", url)
         # If we're in debug mode, and the file as requested exists, then don't change the links
         elif (settings.DEBUG and finders.find(rest, True)):
-            url = match.group('prefix') + rest
-            log.warning("From finder: %s", url)
+            return original
         # Otherwise, look the file up in staticfiles_storage
         else:
             path = data_directory + '/' + rest
             try:
                 url = staticfiles_storage.url(path)
-                log.warning("From staticfiles_storage: %s", url)
             # And if that fails, return the path unmodified
             except Exception as err:
                 log.warning("staticfiles_storage couldn't find path {0}: {1}".format(
                     path, str(err)))
-                url = path
-                log.warning("Fallback: %s", url)
-        log.warning("".join([quote, url, quote]))
+                return original
         return "".join([quote, url, quote])
 
     return re.sub(
diff --git a/common/djangoapps/static_replace/test/test_static_replace.py b/common/djangoapps/static_replace/test/test_static_replace.py
index c451f11ec6..cfc025b964 100644
--- a/common/djangoapps/static_replace/test/test_static_replace.py
+++ b/common/djangoapps/static_replace/test/test_static_replace.py
@@ -1,8 +1,12 @@
 from nose.tools import assert_equals
 from static_replace import replace_static_urls, replace_course_urls
+from mock import patch, Mock
+from xmodule.modulestore import Location
+from xmodule.modulestore.mongo import MongoModuleStore
 
 DATA_DIRECTORY = 'data_dir'
 COURSE_ID = 'org/course/run'
+NAMESPACE = Location('org', 'course', 'run', None, None)
 
 
 def test_multi_replace():
@@ -17,4 +21,36 @@ def test_multi_replace():
         replace_course_urls(course_source, COURSE_ID),
         replace_course_urls(replace_course_urls(course_source, COURSE_ID), COURSE_ID)
     )
-    assert False
+
+
+@patch('static_replace.finders')
+@patch('static_replace.settings')
+def test_debug_no_modify(mock_settings, mock_finders):
+    mock_settings.DEBUG = True
+    mock_finders.find.return_value = True
+
+    static_source = '"/static/file.png"'
+    assert_equals(static_source, replace_static_urls(static_source, DATA_DIRECTORY))
+
+    mock_finders.find.assert_called_once_with('file.png', True)
+
+
+@patch('static_replace.StaticContent')
+@patch('static_replace.modulestore')
+def test_mongo_filestore(mock_modulestore, mock_static_content):
+
+    mock_modulestore.return_value = Mock(MongoModuleStore)
+    mock_static_content.convert_legacy_static_url.return_value = "c4x://mock_url"
+
+    static_source = '"/static/file.png"'
+
+    # No namespace => no change to path
+    assert_equals(static_source, replace_static_urls(static_source, DATA_DIRECTORY))
+
+    # Namespace => content url
+    assert_equals(
+        '"' + mock_static_content.convert_legacy_static_url.return_value + '"',
+        replace_static_urls(static_source, DATA_DIRECTORY, NAMESPACE)
+    )
+
+    mock_static_content.convert_legacy_static_url.assert_called_once_with('file.png', NAMESPACE)