diff --git a/.travis.yml b/.travis.yml
index eb7d5605..90ffd3d4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,7 +13,30 @@ notifications:
 # and an empty 'python' variable in order to prevent that Travis attempts
 # to install Python.
 # TODO: Figure out how specific versions of Python 3.x can be used with OS-X
+
+# When defining the job matrix explicitly, there are Travis environments
+# that produce an additional default job. See these Travis issues:
+#   https://github.com/travis-ci/travis-ci/issues/1228
+#   https://github.com/travis-ci/travis-ci/issues/4681
+#   https://github.com/travis-ci/travis-ci/issues/9843
+# The public Travis does not seem to have this issue anymore,
+# but Travis@IBM does have this issue (as of 9/2018). The workaround for
+# this issue is to define variables globally and to exclude this same
+# variable value in the matrix definition. Experiments have shown that
+# not all variable combinations work. Using a combination of 'language'
+# and 'os' set to the default values works.
+
+# See note about explicit job matrix, above.
+language: ruby
+os: linux
+
 matrix:
+
+  # See note about explicit job matrix, above.
+  exclude:
+    - language: ruby
+    - os: linux
+
   include:
 #    - os: linux
 #      language: python
@@ -105,6 +128,23 @@ matrix:
       cache: pip
 
 before_install:
+  - env | sort
+
+  # The following statement is a workaround to leave an OS-X job
+  # when running on Linux. That happens on Travis@IBM which does not
+  # have OS-X support but still runs os=osx on Linux.
+  - if [[ "$TRAVIS_OS_NAME" == "osx" && "$_system_type" == "Linux" ]]; then
+      echo "Exiting from OS-X job running on Linux";
+      exit;
+    fi
+
+  # The following statement is a safety net in case the matrix exclusion
+  # does not work for some reason.
+  - if [[ "$TRAVIS_LANGUAGE" == "ruby" ]]; then
+      echo "Exiting from unwanted default Ruby job";
+      exit;
+    fi
+
   - if [[ "$TRAVIS_BRANCH" == "manual-ci-run" ]]; then
       export _NEED_REBASE=true;
     fi