diff --git a/test_appendfilename.py b/test_appendfilename.py
index e930c07..a680818 100755
--- a/test_appendfilename.py
+++ b/test_appendfilename.py
@@ -283,7 +283,7 @@ def test_smart_prepend(arg1, arg2, arg3):
         old_filename_no_timestamp = old_filename[8:]
 
     # pattern `--short`  # currently fails
-    elif re.search(r"^\d{4}[012]\d[012]\d", old_filename):
+    elif re.search(r"^\d{4}[012]\d[0-3]\d", old_filename):
         time_stamp = old_filename[:6]
         time_stamp_separator = old_filename[6]
         old_filename_no_timestamp = old_filename[7:]
diff --git a/test_generator.org b/test_generator.org
index fc94086..fe27ac8 100755
--- a/test_generator.org
+++ b/test_generator.org
@@ -467,7 +467,7 @@ def test_smart_prepend(arg1, arg2, arg3):
         old_filename_no_timestamp = old_filename[8:]
 
     # pattern `--short`  # currently fails
-    elif re.search(r"^\d{4}[012]\d[012]\d", old_filename):
+    elif re.search(r"^\d{4}[012]\d[0-3]\d", old_filename):
         time_stamp = old_filename[:6]
         time_stamp_separator = old_filename[6]
         old_filename_no_timestamp = old_filename[7:]