diff --git a/tools/revision.py b/tools/revision.py
index 1096c12dd..1d946029f 100644
--- a/tools/revision.py
+++ b/tools/revision.py
@@ -4,6 +4,7 @@
 
 import svn_util as svn
 import git_util as git
+import os
 import sys
 
 # cannot be loaded as a module
@@ -11,9 +12,11 @@ if __name__ != "__main__":
     sys.stderr.write('This file cannot be loaded as a module!')
     sys.exit()
 
-try:
+if os.path.exists(os.path.join('.', '.svn')):
   sys.stdout.write(svn.get_revision())
-except:
+elif os.path.exists(os.path.join('.', '.git')):
   sys.stdout.write(git.get_svn_revision())
+else:
+  raise Exception('Not a valid checkout')