diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index d214933..d8e891c 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3707,7 +3707,7 @@
     static int
 check_regexp_delim(int c)
 {
-    if (isalpha(c))
+    if (SAFE_isalpha(c))
     {
 	emsg(_(e_regular_expressions_cant_be_delimited_by_letters));
 	return FAIL;