diff --git a/src/filelock.c b/src/filelock.c
index c98afdd30d1..15b0dcb8c73 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -428,6 +428,7 @@ if it should normally be locked.")
 
 /* Unlock the file visited in buffer BUFFER.  */
 
+void
 unlock_buffer (buffer)
      struct buffer *buffer;
 {