diff --git a/src/agents/util/_transforms.py b/src/agents/util/_transforms.py
index b303074d6..2ab07f3de 100644
--- a/src/agents/util/_transforms.py
+++ b/src/agents/util/_transforms.py
@@ -1,11 +1,21 @@
 import re
 
+from ..logger import logger
+
 
 def transform_string_function_style(name: str) -> str:
     # Replace spaces with underscores
     name = name.replace(" ", "_")
 
     # Replace non-alphanumeric characters with underscores
-    name = re.sub(r"[^a-zA-Z0-9]", "_", name)
+    transformed_name = re.sub(r"[^a-zA-Z0-9_]", "_", name)
+
+    if transformed_name != name:
+        final_name = transformed_name.lower()
+        logger.warning(
+            f"Tool name {name!r} contains invalid characters for function calling and has been "
+            f"transformed to {final_name!r}. Please use only letters, digits, and underscores "
+            "to avoid potential naming conflicts."
+        )
 
-    return name.lower()
+    return transformed_name.lower()