diff --git a/oxlib/format.py b/oxlib/format.py
index be7a826..cf7b102 100644
--- a/oxlib/format.py
+++ b/oxlib/format.py
@@ -174,6 +174,8 @@ def formatDuration(ms, verbosity=0, years=True, hours=True, milliseconds=True):
     >>> formatDuration(1000 * 30, hours=False, milliseconds=False)
     '00:30'
     '''
+    if not ms:
+        return ''
     if years:
         y = int(ms / 31536000000)
         d = int(ms % 31536000000 / 86400000)