diff --git a/src/undo.c b/src/undo.c
index a23c263..b9c203c 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -123,6 +123,7 @@
 static void serialize_visualinfo(bufinfo_T *bi, visualinfo_T *info);
 static void unserialize_visualinfo(bufinfo_T *bi, visualinfo_T *info);
 #endif
+static void u_saveline(linenr_T lnum);
 
 #define U_ALLOC_LINE(size) lalloc(size, FALSE)
 
@@ -3435,7 +3436,7 @@
 /*
  * Save the line "lnum" for the "U" command.
  */
-    void
+    static void
 u_saveline(linenr_T lnum)
 {
     if (lnum == curbuf->b_u_line_lnum)	    /* line is already saved */