diff --git a/src/tool_main.c b/src/tool_main.c
index e0766e9b7d0aa1def31b352ddd91b6b84b0e1485..5682bd78e976bd4e02402a8db967698b544dd273 100644
--- a/src/tool_main.c
+++ b/src/tool_main.c
@@ -84,7 +84,7 @@ static void main_checkfds(void)
 }
 
 #ifdef CURLDEBUG
-void memory_tracking_init(void)
+static void memory_tracking_init(void)
 {
   char *env;
   /* if CURL_MEMDEBUG is set, this starts memory tracking message logging */