diff --git a/mk/tests.mk b/mk/tests.mk
index 0f69ddf2d7f..2599e1a6272 100644
--- a/mk/tests.mk
+++ b/mk/tests.mk
@@ -25,7 +25,7 @@ $(eval $(call RUST_CRATE,collectionstest))
 TEST_TARGET_CRATES = $(filter-out core rustc_unicode alloc_system libc \
 		     		  alloc_jemalloc,$(TARGET_CRATES)) \
 			collectionstest coretest
-TEST_DOC_CRATES = $(DOC_CRATES) arena
+TEST_DOC_CRATES = $(DOC_CRATES) arena flate
 TEST_HOST_CRATES = $(filter-out rustc_typeck rustc_borrowck rustc_resolve \
 		   		rustc_trans rustc_lint,\
                      $(HOST_CRATES))
diff --git a/src/libflate/lib.rs b/src/libflate/lib.rs
index 51f38752329..513379b6558 100644
--- a/src/libflate/lib.rs
+++ b/src/libflate/lib.rs
@@ -23,7 +23,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(attr(deny(warnings))))]
 
 #![feature(libc)]
 #![feature(staged_api)]