diff --git a/arch/x86/um/ldt.c b/arch/x86/um/ldt.c
index 3ee234b6234dd..255a44dd415a9 100644
--- a/arch/x86/um/ldt.c
+++ b/arch/x86/um/ldt.c
@@ -23,9 +23,11 @@ static long write_ldt_entry(struct mm_id *mm_idp, int func,
 {
 	long res;
 	void *stub_addr;
+
+	BUILD_BUG_ON(sizeof(*desc) % sizeof(long));
+
 	res = syscall_stub_data(mm_idp, (unsigned long *)desc,
-				(sizeof(*desc) + sizeof(long) - 1) &
-				    ~(sizeof(long) - 1),
+				sizeof(*desc) / sizeof(long),
 				addr, &stub_addr);
 	if (!res) {
 		unsigned long args[] = { func,