diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index b69bdeb4b9febdb9b6446e56138cbebcfa791914..1e9e3c4705611792f2423cad1682c494b9332bc5 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -35,7 +35,7 @@ static ssize_t read_text(const char *path, char *buf, size_t max_len)
 	return len;
 }
 
-static ssize_t write_text(const char *path, char *buf, size_t len)
+static ssize_t write_text(const char *path, char *buf, ssize_t len)
 {
 	int fd;
 
@@ -140,7 +140,7 @@ long cg_read_key_long(const char *cgroup, const char *control, const char *key)
 int cg_write(const char *cgroup, const char *control, char *buf)
 {
 	char path[PATH_MAX];
-	size_t len = strlen(buf);
+	ssize_t len = strlen(buf);
 
 	snprintf(path, sizeof(path), "%s/%s", cgroup, control);