diff --git a/test/simple-xinit.c b/test/simple-xinit.c
index 1fc31be26..26ff12bf7 100644
--- a/test/simple-xinit.c
+++ b/test/simple-xinit.c
@@ -87,7 +87,7 @@ get_display(int displayfd)
     char display_string[10];
     ssize_t ret;
 
-    ret = read(displayfd, display_string, sizeof(display_string - 1));
+    ret = read(displayfd, display_string, sizeof(display_string) - 1);
     if (ret <= 0) {
         fprintf(stderr, "Failed reading displayfd: %s\n", strerror(errno));
         exit(1);