diff --git a/admin/autoupdater/src/autoupdater.c b/admin/autoupdater/src/autoupdater.c
index dcf8829..8d8bc74 100644
--- a/admin/autoupdater/src/autoupdater.c
+++ b/admin/autoupdater/src/autoupdater.c
@@ -380,10 +380,12 @@ static bool autoupdate(const char *mirror, struct settings *s, int lock_fd) {
 
 	/* Test the image upgrade (issue #193) */
 	{
+		static const char *const exec_builtin = "exec ";
 		static const char *const test_option = " --test ";
 
-		char buf[strlen(sysupgrade_path) + strlen(test_option) + strlen(firmware_path) + 1];
-		strcpy(buf, sysupgrade_path);
+		char buf[strlen(exec_builtin) + strlen(sysupgrade_path) + strlen(test_option) + strlen(firmware_path) + 1];
+		strcpy(buf, exec_builtin);
+		strcat(buf, sysupgrade_path);
 		strcat(buf, test_option);
 		strcat(buf, firmware_path);