diff --git a/src/evalvars.c b/src/evalvars.c
index 197a19d..e2469b0 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -3849,6 +3849,27 @@
 }
 
 /*
+ * Copy callback from "src" to "dest", incrementing the refcounts.
+ */
+    void
+copy_callback(callback_T *dest, callback_T *src)
+{
+    dest->cb_partial = src->cb_partial;
+    if (dest->cb_partial != NULL)
+    {
+	dest->cb_name = src->cb_name;
+	dest->cb_free_name = FALSE;
+	++dest->cb_partial->pt_refcount;
+    }
+    else
+    {
+	dest->cb_name = vim_strsave(src->cb_name);
+	dest->cb_free_name = TRUE;
+	func_ref(src->cb_name);
+    }
+}
+
+/*
  * Unref/free "callback" returned by get_callback() or set_callback().
  */
     void