diff --git a/exec/crypto.c b/exec/crypto.c
index 572c1661..e943bc4a 100644
--- a/exec/crypto.c
+++ b/exec/crypto.c
@@ -37,8 +37,8 @@ typedef uint64_t ulong64;
 #define ENDIAN_LITTLE
 #elif _BYTE_ORDER == _BIG_ENDIAN
 #define ENDIAN_BIG
-#elif
-#warning "cannot detect byte order"
+#else
+#error "cannot detect byte order"
 #endif
 
 #if defined(COROSYNC_LINUX)