Index: stamper/stamper.py
===================================================================
--- stamper/stamper.py	(revision 32)
+++ stamper/stamper.py	(revision 36)
@@ -128,7 +128,12 @@
         else:
             # maybe they are giving us a fixed date
-            filter_from = datetime.strptime(stamp_filter, DATE_FORMAT)
-            filter_from = filter_from.replace(hour=0, minute=0, second=0)
-            filter_to = filter_from + timedelta(days=1)
+            try:
+                filter_from = datetime.strptime(stamp_filter, DATE_FORMAT)
+            except:
+                # nothing to be used as a filter, go on, printing a warning
+                print('[warning] invalid date filter: ' + stamp_filter)
+            else:
+                filter_from = filter_from.replace(hour=0, minute=0, second=0)
+                filter_to = filter_from + timedelta(days=1)
 
         return filter_from, filter_to