diff --git a/build_tools/check.sh b/build_tools/check.sh
index 67556a190..3252f5476 100755
--- a/build_tools/check.sh
+++ b/build_tools/check.sh
@@ -29,8 +29,8 @@ cleanup () {
 trap cleanup EXIT INT TERM HUP
 
 if $lint; then
-    export RUSTFLAGS='-D warnings'
-    export RUSTDOCFLAGS='-D warnings'
+    export RUSTFLAGS="--deny=warnings ${RUSTFLAGS}"
+    export RUSTDOCFLAGS="--deny=warnings ${RUSTDOCFLAGS}"
 fi
 
 repo_root="$(dirname "$0")/.."