diff --git a/src/regexp.c b/src/regexp.c
index 3d08d5a..0a6a8af 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -22,7 +22,7 @@
 
 #ifdef FEAT_RELTIME
 static int dummy_timeout_flag = 0;
-static const int *timeout_flag = &dummy_timeout_flag;
+static volatile int *timeout_flag = &dummy_timeout_flag;
 #endif
 
 /*