diff --git a/.travis.yml b/.travis.yml
index 407fec9..7d68ec1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,8 +2,7 @@ language: python
 python: "2.7"
 env:
     global:
-        - IS_TRAVIS=true  # used by owncloud-testserver to install php
-        - CFLAGS=-O0  # speed up lxml build
+        - IS_TRAVIS=true
     matrix:
         - DAV_SERVER=radicale_filesystem REQUIREMENTS=release
         - DAV_SERVER=radicale_filesystem REQUIREMENTS=devel
diff --git a/install-deps.sh b/install-deps.sh
index bf84ce0..aa11575 100755
--- a/install-deps.sh
+++ b/install-deps.sh
@@ -4,12 +4,13 @@ set -e
 [ -n "$DAV_SERVER" ] || DAV_SERVER=radicale_filesystem
 [ -n "$REQUIREMENTS" ] || REQUIREMENTS=release
 
+PIP_INSTALL="pip install"
 if [ "$IS_TRAVIS" = "true" ]; then
+    export CFLAGS=-O0  # speed up builds of packages which don't have wheels
     PIP_INSTALL="pip install --use-wheel --find-links=http://dev.unterwaditzer.net/vdirsyncer/wheels/"
     pip install --upgrade wheel pip setuptools
-else
-    PIP_INSTALL="pip install"
 fi
+
 $PIP_INSTALL --editable .
 $PIP_INSTALL -r requirements.txt