diff --git a/gio/gfiledescriptorbased.c b/gio/gfiledescriptorbased.c
index 5ebdf6eca..2647a9b8e 100644
--- a/gio/gfiledescriptorbased.c
+++ b/gio/gfiledescriptorbased.c
@@ -63,7 +63,7 @@ g_file_descriptor_based_get_fd (GFileDescriptorBased *fd_based)
 {
   GFileDescriptorBasedIface *iface;
 
-  g_return_val_if_fail (G_IS_FILE_DESCRIPTOR_BASED (fd_based), 0);
+  g_return_val_if_fail (G_IS_FILE_DESCRIPTOR_BASED (fd_based), -1);
 
   iface = G_FILE_DESCRIPTOR_BASED_GET_IFACE (fd_based);