diff --git a/bin/work b/bin/work
index c24713c..bae7f33 100755
--- a/bin/work
+++ b/bin/work
@@ -43,10 +43,14 @@ def signal_handler(signal, frame):
 
 
 def td_format(td):
+    prefix = ""
+    if td < timedelta(0):
+        td = -td
+        prefix = "-"
     hours, remainder = divmod(td.total_seconds(), 3600)
     minutes, seconds = divmod(remainder, 60)
 
-    return '{:d}:{:02d}'.format(int(hours), int(minutes))
+    return '{}{:d}:{:02d}'.format(prefix, int(hours), int(minutes))
 
 
 def get_today_fields():