diff --git a/lib/galaxy/tool_util/deps/requirements.py b/lib/galaxy/tool_util/deps/requirements.py
index c7bd3f854081..d2fbb249aa63 100644
--- a/lib/galaxy/tool_util/deps/requirements.py
+++ b/lib/galaxy/tool_util/deps/requirements.py
@@ -195,8 +195,8 @@ def __init__(
         if identifier:
             parts = identifier.rsplit(os.sep, 1)
             if ":" in parts[-1]:
-                id, tag = parts[-1].rsplit(":")
-                parts[-1] = f"{id.lower()}:{tag}"
+                name, tag = parts[-1].rsplit(":", 1)
+                parts[-1] = f"{name.lower()}:{tag}"
             else:
                 parts[-1] = parts[-1].lower()