diff --git a/src/boot/efi/sha256.c b/src/boot/efi/sha256.c
index 774f0eeb6c..2108ea29c7 100644
--- a/src/boot/efi/sha256.c
+++ b/src/boot/efi/sha256.c
@@ -143,9 +143,12 @@ void sha256_process_bytes(const void *buffer, UINTN len, struct sha256_ctx *ctx)
 
         /* Process available complete blocks.  */
         if (len >= 64) {
-#if !_STRING_ARCH_unaligned
-/* To check alignment gcc has an appropriate operator.  Other
-   compilers don't.  */
+
+/* The condition below is from glibc's string/string-inline.c.
+ * See definition of _STRING_INLINE_unaligned. */
+#if !defined(__mc68020__) && !defined(__s390__) && !defined(__i386__)
+
+/* To check alignment gcc has an appropriate operator. Other compilers don't.  */
 # if __GNUC__ >= 2
 #  define UNALIGNED_P(p) (((UINTN) p) % __alignof__ (UINT32) != 0)
 # else