diff --git a/test/zdtm/static/fdt_shared.c b/test/zdtm/static/fdt_shared.c
index b1c74d0ae..2111356f5 100644
--- a/test/zdtm/static/fdt_shared.c
+++ b/test/zdtm/static/fdt_shared.c
@@ -62,7 +62,7 @@ static pid_t clone_child(int (*fn)(void *), int flags)
 
 static int child2(void *_arg)
 {
-	char buf[10];
+	char buf[sizeof(TEST_STRING)];
 
 	forked();
 	test_waitsig();
@@ -90,7 +90,7 @@ static int child3(void *_arg)
 
 static int child(void *_arg)
 {
-	char buf[10];
+	char buf[sizeof(TEST_STRING)];
 	pid_t pid, pid2;
 	int status;