diff --git a/drb-c2-core/app/routers/upload.py b/drb-c2-core/app/routers/upload.py
index 008912e..a6436f2 100644
--- a/drb-c2-core/app/routers/upload.py
+++ b/drb-c2-core/app/routers/upload.py
@@ -71,14 +71,15 @@ async def upload_call_audio(
 
 def _public_url_to_gcs_uri(url: str) -> Optional[str]:
     """
-    Convert a public GCS URL like
-      https://storage.googleapis.com/bucket/calls/file.mp3
+    Convert a public GCS URL (possibly signed) like
+      https://storage.googleapis.com/bucket/calls/file.mp3?Expires=...
     to a gs:// URI usable by Speech-to-Text.
     Returns None if the URL doesn't look like a GCS URL.
     """
     prefix = "https://storage.googleapis.com/"
     if url and url.startswith(prefix):
-        return "gs://" + url[len(prefix):]
+        path = url[len(prefix):].split("?")[0]  # strip signed-URL query params
+        return "gs://" + path
     return None