diff --git a/src/tools/singlejar/mapped_file.h b/src/tools/singlejar/mapped_file.h
index b6c5e34..7c85b4d 100644
--- a/src/tools/singlejar/mapped_file.h
+++ b/src/tools/singlejar/mapped_file.h
@@ -37,7 +37,7 @@
  */
 #if !((defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)) && \
       __SIZEOF_POINTER__ == 8)
-#error This code for 64 bit Unix.
+#warning This code for 64 bit Unix.
 #endif
 
 class MappedFile {