--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -198,7 +198,9 @@
   uint8x16_t v = vld1q_dup_u8(&val);
   vst1q_u8(dup, v);
   return 0;
-}" SNAPPY_HAVE_NEON)
+}
+#error
+" SNAPPY_HAVE_NEON)
 
 include(CheckSymbolExists)
 check_symbol_exists("mmap" "sys/mman.h" HAVE_FUNC_MMAP)