diff --git a/src/liblzma/api/lzma/filter.h b/src/liblzma/api/lzma/filter.h
index 04825c65..5ec9976d 100644
--- a/src/liblzma/api/lzma/filter.h
+++ b/src/liblzma/api/lzma/filter.h
@@ -120,7 +120,8 @@ extern LZMA_API(lzma_bool) lzma_filter_decoder_is_supported(lzma_vli id)
  */
 extern LZMA_API(lzma_ret) lzma_filters_copy(
 		const lzma_filter *src, lzma_filter *dest,
-		const lzma_allocator *allocator) lzma_nothrow;
+		const lzma_allocator *allocator)
+		lzma_nothrow lzma_attr_warn_unused_result;
 
 
 /**