diff --git a/bssl-compat/third_party/boringssl/src/include/openssl/base.h b/bssl-compat/third_party/boringssl/src/include/openssl/base.h
index 190e250ff0..dfacda574e 100644
--- a/bssl-compat/third_party/boringssl/src/include/openssl/base.h
+++ b/bssl-compat/third_party/boringssl/src/include/openssl/base.h
@@ -116,6 +116,8 @@ extern "C" {
 #define OPENSSL_32_BIT
 #elif defined(__myriad2__)
 #define OPENSSL_32_BIT
+#elif defined(__s390__) || defined(__s390x__) || defined(__zarch__)
+#define OPENSSL_64_BIT
 #else
 // Note BoringSSL only supports standard 32-bit and 64-bit two's-complement,
 // little-endian architectures. Functions will not produce the correct answer