diff --git a/build.sh b/build.sh
index 2b961e1..00c9b5e 100755
--- a/build.sh
+++ b/build.sh
@@ -28,9 +28,11 @@ install_build_tests() {
 }
 
 run_build_tests() {
-    coverage run --source=vdirsyncer/,tests/ --module pytest
     if [ "$TRAVIS" = "true" ]; then
+        coverage run --source=vdirsyncer/,tests/ --module pytest
         coveralls
+    else
+        py.test
     fi
 }
 
@@ -42,11 +44,34 @@ run_build_style() {
     flake8 vdirsyncer tests
 }
 
+install_build_docs() {
+    $PIP_INSTALL sphinx sphinx_rtd_theme
+    $PIP_INSTALL -e .
+}
+
+run_build_docs() {
+    cd docs
+    make html
+}
+
 
 [ -n "$BUILD" ] || BUILD=tests
 [ -n "$DAV_SERVER" ] || DAV_SERVER=radicale
 [ -n "$REQUIREMENTS" ] || REQUIREMENTS=release
 COMMAND="$1"
+if [ -z "$COMMAND" ]; then
+    echo "Usage:"
+    echo "build.sh run      # run build"
+    echo "build.sh install  # install dependencies"
+    echo
+    echo "Environment variable combinations:"
+    echo "BUILD=tests  # install and run tests"
+    echo "             # (using Radicale, see .travis.yml for more)"
+    echo "BUILD=style  # install and run stylechecker (flake8)"
+    echo "BUILD=docs   # install sphinx and build HTML docs"
+    exit 1
+fi
+
 TESTSERVER_BASE=./tests/storage/dav/servers/
 
 install_builds() {
diff --git a/docs/conf.py b/docs/conf.py
index a043b1b..52a96e4 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -28,7 +28,14 @@ version = '.'.join(release.split('.')[:2])  # The short X.Y version.
 exclude_patterns = ['_build']
 
 pygments_style = 'sphinx'
-html_theme = 'default'
+
+import os
+on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+
+if not on_rtd:
+    import sphinx_rtd_theme
+    html_theme = 'sphinx_rtd_theme'
+    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 html_static_path = ['_static']
 htmlhelp_basename = 'vdirsyncerdoc'