diff --git a/utils.py b/utils.py
index 9b10af6005bf0fde8039d19ec1fe6dc4e637bc9e..7cbb3d8b5f1b29f97a72126ef80420aa46bd623a 100644
--- a/utils.py
+++ b/utils.py
@@ -40,7 +40,7 @@ def npmat_truncate_cols(mat, max_cols):
 def get_id_prefix_from_string(s):
     first_illegal_char_index = 0
     for i, c in enumerate(s):
-        if c not in 'QWERTYUIOPASDFGHJKLZXCVBNM1234567890qwertyuiopasdfghjklzxcvbnm-':
+        if c not in 'QWERTYUIOPASDFGHJKLZXCVBNM1234567890qwertyuiopasdfghjklzxcvbnm-.':
             break
         else:
             first_illegal_char_index = i + 1