diff --git a/django/contrib/postgres/indexes.py b/django/contrib/postgres/indexes.py
index a5c127e942..677c63b4a2 100644
--- a/django/contrib/postgres/indexes.py
+++ b/django/contrib/postgres/indexes.py
@@ -96,5 +96,5 @@ class GistIndex(PostgresIndex):
         if self.buffering is not None:
             with_params.append('buffering = %s' % ('on' if self.buffering else 'off'))
         if self.fillfactor is not None:
-            with_params.append('fillfactor = %s' % self.fillfactor)
+            with_params.append('fillfactor = %d' % self.fillfactor)
         return with_params