diff --git a/test/support/travisci_deps.sh b/test/support/travisci_deps.sh
index d4523ee..83cc32e 100755
--- a/test/support/travisci_deps.sh
+++ b/test/support/travisci_deps.sh
@@ -7,8 +7,26 @@
 #
 # Note: $TRAVIS_OS_NAME will only be set on text boxes with multi-os enabled,
 # so use negation test so it will fail gracefully on normal Travis linux setup.
-#
-# TODO: also perhaps later only on ZSH test box if we split those
 if [[ "$TRAVIS_OS_NAME" != "osx" ]]; then
-  sudo apt-get install zsh
+
+  # okay, so we know we're probably on a linux box (or at least not an osx box)
+  # at this point. do we need to install zsh? let's say the default case is no:
+  needs_zsh=false
+
+  # check if zsh is listed in the TEST_SHELLS environment variable, set by
+  # our travis-ci build matrix.
+  if [[ $TEST_SHELLS =~ zsh ]]; then needs_zsh=true; fi
+
+  # if there is NO $TEST_SHELLS env variable persent (which should never happen,
+  # but maybe someone has been monkeying with the .travis.yml), run_tests.sh is
+  # going to fall back onto the default of testing everything, so we need zsh.
+  if [[ -z "$TEST_SHELLS" ]]; then needs_zsh=true; fi
+
+  # finally, we install zsh if needed!
+  if $needs_zsh ; then
+    sudo apt-get install zsh
+  else
+    echo "No deps required."
+  fi
+
 fi