diff --git a/langfun/core/data/conversion/gemini.py b/langfun/core/data/conversion/gemini.py
index 5620e6da..cba207c3 100644
--- a/langfun/core/data/conversion/gemini.py
+++ b/langfun/core/data/conversion/gemini.py
@@ -83,12 +83,14 @@ def _convert_chunk(
       if video_metadata:
         result['videoMetadata'] = video_metadata
       return result
+    if chunk.uri and chunk.uri.startswith('gs://'):
+      always_send_content = False
     if chunk.is_text:
       return {'text': chunk.to_text()}
     if (
         not always_send_content
         and chunk.uri
-        and chunk.uri.lower().startswith(('http:', 'https:', 'ftp:'))
+        and chunk.uri.lower().startswith(('http:', 'https:', 'ftp:', 'gs:'))
     ):
       return {
           'fileData': {
diff --git a/langfun/core/data/conversion/gemini_test.py b/langfun/core/data/conversion/gemini_test.py
index 33489cbd..c37364f6 100644
--- a/langfun/core/data/conversion/gemini_test.py
+++ b/langfun/core/data/conversion/gemini_test.py
@@ -92,6 +92,30 @@ def test_as_format_with_image(self):
         },
     )
 
+  def test_as_format_with_gcs_uri(self):
+    self.assertEqual(
+        lf.Template(
+            'Summarize {{doc}}',
+            doc=lf_modalities.Custom.from_uri(
+                'gs://my-bucket/temp/doc.pdf', mime='application/pdf'
+            ),
+        )
+        .render()
+        .as_gemini_format(),
+        {
+            'role': 'user',
+            'parts': [
+                {'text': 'Summarize'},
+                {
+                    'fileData': {
+                        'fileUri': 'gs://my-bucket/temp/doc.pdf',
+                        'mimeType': 'application/pdf',
+                    }
+                },
+            ],
+        },
+    )
+
   def test_as_format_youtube_with_video_metadata(self):
     self.assertEqual(
         lf.Template(