diff --git a/.travis.yml b/.travis.yml
index 09ef5985..c5ffd833 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,7 +19,7 @@ env:
   - SIX_VERSION=1.9 USE_OPTIONAL=true
 
 install:
-  - bash requirements-install.sh
+  - ./requirements-install.sh
 
 script:
   - if [[ $TRAVIS_PYTHON_VERSION == pypy* ]]; then py.test; fi
diff --git a/requirements-install.sh b/requirements-install.sh
index 0be226a6..7ba9396f 100755
--- a/requirements-install.sh
+++ b/requirements-install.sh
@@ -1,9 +1,6 @@
-#!/bin/bash -e
+#!/bin/bash -ex
 
-if [[ $USE_OPTIONAL != "true" && $USE_OPTIONAL != "false" ]]; then
-  echo "fatal: \$USE_OPTIONAL not set to true or false. Exiting."
-  exit 1
-fi
+pip install pip==6.1.0
 
 pip install -U -r requirements-test.txt
 
@@ -11,7 +8,7 @@ if [[ $USE_OPTIONAL == "true" ]]; then
   pip install -U -r requirements-optional.txt
 fi
 
-if [[ $SIX_VERSION != "false" ]]; then
+if [[ $SIX_VERSION ]]; then
   pip install six==$SIX_VERSION
 fi