diff --git a/kallithea/lib/celerylib/__init__.py b/kallithea/lib/celerylib/__init__.py
--- a/kallithea/lib/celerylib/__init__.py
+++ b/kallithea/lib/celerylib/__init__.py
@@ -28,7 +28,7 @@ Original author and date, and relevant c
 
 import logging
 import os
-from hashlib import md5
+from hashlib import sha1
 
 from decorator import decorator
 from tg import config
@@ -94,7 +94,7 @@ def __get_lockkey(func, *fargs, **fkwarg
     func_name = str(func.__name__) if hasattr(func, '__name__') else str(func)
 
     lockkey = 'task_%s.lock' % \
-        md5(safe_bytes(func_name + '-' + '-'.join(str(x) for x in params))).hexdigest()
+        sha1(safe_bytes(func_name + '-' + '-'.join(str(x) for x in params))).hexdigest()
     return lockkey
 
 
diff --git a/kallithea/lib/markup_renderer.py b/kallithea/lib/markup_renderer.py
--- a/kallithea/lib/markup_renderer.py
+++ b/kallithea/lib/markup_renderer.py
@@ -74,13 +74,13 @@ class MarkupRenderer(object):
 
         :param text:
         """
-        from hashlib import md5
+        from hashlib import sha1
 
         # Extract pre blocks.
         extractions = {}
 
         def pre_extraction_callback(matchobj):
-            digest = md5(matchobj.group(0)).hexdigest()
+            digest = sha1(matchobj.group(0)).hexdigest()
             extractions[digest] = matchobj.group(0)
             return "{gfm-extraction-%s}" % digest
         pattern = re.compile(r'<pre>.*?</pre>', re.MULTILINE | re.DOTALL)