diff --git a/src/evalvars.c b/src/evalvars.c
index f7939cb..779627c 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -648,7 +648,7 @@
  * Used for a heredoc assignment.
  * Returns NULL for an error.
  */
-    char_u *
+    static char_u *
 eval_all_expr_in_str(char_u *str)
 {
     garray_T	ga;