diff --git a/fin_defs/__init__.py b/fin_defs/__init__.py
index bba5de2..9e66851 100644
--- a/fin_defs/__init__.py
+++ b/fin_defs/__init__.py
@@ -10,7 +10,7 @@ import enforce_typing
 ## Ids
 
 RE_TICKER_FORMAT = r'^[A-Z0-9_]+$'
-RE_TICKER_FORMAT_FLEXIBLE = r'^[^:\s]+$'
+RE_TICKER_FORMAT_FLEXIBLE = r'^[^:\s](?:[^:]*[^:\s])?$'
 RE_CRYPTO_TICKER_FORMAT = r'^\S+$'