diff --git a/tools/travis_script.sh b/tools/travis_script.sh
index 9810f855..b5d3141a 100755
--- a/tools/travis_script.sh
+++ b/tools/travis_script.sh
@@ -9,7 +9,8 @@ section_end "Test.with.min.requirements"
 
 section "Build.docs"
 if [[ ($PY != 2.6) && ($PY != 3.2) ]]; then
-    SPHINXBUILD="python $(which sphinx-build) -d $HOME/.cache/sphinx" make html
+    export SPHINXBUILD="python $(which sphinx-build) -d $HOME/.cache/sphinx"
+    make html
 fi
 section_end "Build.docs"