diff --git a/library/sha256.c b/library/sha256.c
index ca3fa5d..13fb679 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -35,6 +35,11 @@
  * at the top of this file, before any includes.
  */
 #define __ARM_FEATURE_CRYPTO 1
+/* See: https://arm-software.github.io/acle/main/acle.html#cryptographic-extensions
+ *
+ * `__ARM_FEATURE_CRYPTO` is deprecated. Reserve it for older compilers.
+ */
+#define __ARM_FEATURE_SHA2   1
 #define NEED_TARGET_OPTIONS
 #endif /* __aarch64__ && __clang__ &&
           !__ARM_FEATURE_CRYPTO && __clang_major__ < 18 && __clang_major__ > 3 */