diff --git a/.travis.yml b/.travis.yml
index d67a514c5edb..1354e724483e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,11 +20,11 @@ matrix:
         - export LLVM_CONFIG=/usr/lib/llvm-3.9/bin/llvm-config
         - export CC=gcc-5 CXX=g++-5
       script:
-         - RUSTFLAGS='-D warnings' ./mach build -d --verbose
-         - RUSTFLAGS='-D warnings' ./mach test-unit
+         - ./mach build -d --verbose
+         - ./mach test-unit
          - ./mach clean
-         - RUSTFLAGS='-D warnings' ./mach build-geckolib
-         - RUSTFLAGS='-D warnings' ./mach test-stylo
+         - ./mach build-geckolib
+         - ./mach test-stylo
          - bash etc/ci/lockfile_changed.sh
       cache:
         directories:
@@ -34,7 +34,9 @@ matrix:
       before_cache:
         - ./mach clean-nightlies --keep 2 --force
         - ./mach clean-cargo-cache --keep 2 --force
-      env: CCACHE=/usr/bin/ccache
+      env:
+        CCACHE=/usr/bin/ccache
+        RUSTFLAGS=-Dwarnings
       addons:
         apt:
           sources:
diff --git a/appveyor.yml b/appveyor.yml
index dbb4772330e3..841213809578 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -3,6 +3,7 @@ version: 1.0.{build}
 environment:
   CCACHE_DIR: "%APPVEYOR_BUILD_FOLDER%\\.ccache"
   RUST_BACKTRACE: 1
+  RUSTFLAGS: -Dwarnings
   # The appveyor image we use has a pretty huge set of things installed... we make the
   # initial PATH something sane so we know what to expect
   PATH: "C:\\windows\\system32;\
@@ -48,7 +49,6 @@ cache:
 #  - ps: $blockRdp = $true; iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))
 
 build_script:
-  - set RUSTFLAGS=-D warnings
   - mach build -d -v
   - mach test-unit
 
diff --git a/etc/ci/buildbot_steps.yml b/etc/ci/buildbot_steps.yml
index 97ef5d4d78c8..62ba5177841d 100644
--- a/etc/ci/buildbot_steps.yml
+++ b/etc/ci/buildbot_steps.yml
@@ -1,3 +1,6 @@
+env:
+  RUSTFLAGS: -Dwarnings
+
 mac-rel-wpt1:
   - ./mach clean-nightlies --keep 3 --force
   - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig ./mach build --release
@@ -32,11 +35,11 @@ mac-rel-wpt4:
 
 mac-dev-unit:
   - ./mach clean-nightlies --keep 3 --force
-  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig RUSTFLAGS=-Dwarnings ./mach build --dev
-  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig RUSTFLAGS=-Dwarnings ./mach test-unit
-  - env ./mach package --dev
-  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig RUSTFLAGS=-Dwarnings ./mach build-cef
-  - env RUSTFLAGS=-Dwarnings ./mach build-geckolib
+  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig ./mach build --dev
+  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig ./mach test-unit
+  - ./mach package --dev
+  - env PKG_CONFIG_PATH=/usr/local/opt/zlib/lib/pkgconfig ./mach build-cef
+  - ./mach build-geckolib
   - bash ./etc/ci/lockfile_changed.sh
   - bash ./etc/ci/manifest_changed.sh
 
@@ -80,13 +83,13 @@ linux-dev:
   - ./mach clean-nightlies --keep 3 --force
   - ./mach test-tidy --no-progress --all
   - ./mach test-tidy --no-progress --self-test
-  - env CC=gcc-5 CXX=g++-5 RUSTFLAGS=-Dwarnings ./mach build --dev
-  - env CC=gcc-5 CXX=g++-5 RUSTFLAGS=-Dwarnings ./mach test-unit
-  - env ./mach package --dev
-  - env CC=gcc-5 CXX=g++-5 RUSTFLAGS=-Dwarnings ./mach build-cef
-  - env CC=gcc-5 CXX=g++-5 RUSTFLAGS=-Dwarnings ./mach build --dev --no-default-features --features default-except-unstable
-  - env RUSTFLAGS=-Dwarnings ./mach build-geckolib
-  - env RUSTFLAGS=-Dwarnings ./mach test-stylo
+  - env CC=gcc-5 CXX=g++-5 ./mach build --dev
+  - env CC=gcc-5 CXX=g++-5 ./mach test-unit
+  - ./mach package --dev
+  - env CC=gcc-5 CXX=g++-5 ./mach build-cef
+  - env CC=gcc-5 CXX=g++-5 ./mach build --dev --no-default-features --features default-except-unstable
+  - ./mach build-geckolib
+  - ./mach test-stylo
   - bash ./etc/ci/lockfile_changed.sh
   - bash ./etc/ci/manifest_changed.sh
   - bash ./etc/ci/check_no_panic.sh
@@ -120,7 +123,7 @@ linux-nightly:
 
 android:
   - ./mach clean-nightlies --keep 3 --force
-  - env ANDROID_SDK=/home/servo/android/sdk/r25.2.3 RUSTFLAGS=-Dwarnings ./mach build --android --dev
+  - env ANDROID_SDK=/home/servo/android/sdk/r25.2.3 ./mach build --android --dev
   - env ANDROID_SDK=/home/servo/android/sdk/r25.2.3 ./mach package --android --dev
   - bash ./etc/ci/lockfile_changed.sh
   - bash ./etc/ci/manifest_changed.sh
@@ -134,19 +137,18 @@ android-nightly:
 
 arm32:
   - ./mach clean-nightlies --keep 3 --force
-  - env RUSTFLAGS=-Dwarnings ./mach build --rel --target=arm-unknown-linux-gnueabihf
+  - ./mach build --rel --target=arm-unknown-linux-gnueabihf
   - bash ./etc/ci/lockfile_changed.sh
   - bash ./etc/ci/manifest_changed.sh
 
 arm64:
   - ./mach clean-nightlies --keep 3 --force
-  - env RUSTFLAGS=-Dwarnings ./mach build --rel --target=aarch64-unknown-linux-gnu
+  - ./mach build --rel --target=aarch64-unknown-linux-gnu
   - bash ./etc/ci/lockfile_changed.sh
   - bash ./etc/ci/manifest_changed.sh
 
 windows-msvc-dev:
   - mach.bat clean-nightlies --keep 3 --force
-  - set RUSTFLAGS=-D warnings
   - mach.bat build --dev
   - mach.bat test-unit
   - mach.bat package --dev