diff --git a/.travis.yml b/.travis.yml
index 50d63e593..ac00ef918 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -22,10 +22,17 @@ env:
     # 64-bit Clang 3.9 RelWithDebInfo
     - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/clang-3.9 CXX_COMPILER=/usr/bin/clang++-3.9 TARGET_ARCH=x86_64 Z3_BUILD_TYPE=RelWithDebInfo
 
+    # Debug builds
+    #
+    # Note the unit tests for the debug builds are compiled but **not**
+    # executed. This is because the debug build of unit tests takes a large
+    # amount of time to execute compared to the optimized builds. The hope is
+    # that just running the optimized unit tests is sufficient.
+    #
     # 64-bit GCC 5.4 Debug
-    - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/gcc-5 CXX_COMPILER=/usr/bin/g++-5 TARGET_ARCH=x86_64 Z3_BUILD_TYPE=Debug
+    - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/gcc-5 CXX_COMPILER=/usr/bin/g++-5 TARGET_ARCH=x86_64 Z3_BUILD_TYPE=Debug RUN_UNIT_TESTS=BUILD_ONLY
     # 64-bit Clang Debug
-    - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/clang-3.9 CXX_COMPILER=/usr/bin/clang++-3.9 TARGET_ARCH=x86_64 Z3_BUILD_TYPE=Debug
+    - LINUX_BASE=ubuntu_16.04 C_COMPILER=/usr/bin/clang-3.9 CXX_COMPILER=/usr/bin/clang++-3.9 TARGET_ARCH=x86_64 Z3_BUILD_TYPE=Debug RUN_UNIT_TESTS=BUILD_ONLY
 
     # 32-bit GCC 5.4 RelWithDebInfo
     - LINUX_BASE=ubuntu32_16.04 C_COMPILER=/usr/bin/gcc-5 CXX_COMPILER=/usr/bin/g++-5 TARGET_ARCH=i686 Z3_BUILD_TYPE=RelWithDebInfo
diff --git a/contrib/ci/README.md b/contrib/ci/README.md
index 2e117c8b1..e4c9aecfd 100644
--- a/contrib/ci/README.md
+++ b/contrib/ci/README.md
@@ -31,7 +31,7 @@ the future.
 * `NO_SUPPRESS_OUTPUT` - Don't suppress output of some commands (`0` or `1`)
 * `PYTHON_BINDINGS` - Build and test Python API bindings (`0` or `1`)
 * `RUN_SYSTEM_TESTS` - Run system tests (`0` or `1`)
-* `RUN_UNIT_TESTS` - Run unit tests (`0` or `1`)
+* `RUN_UNIT_TESTS` - Run unit tests (`BUILD_ONLY` or `BUILD_AND_RUN` or `SKIP`)
 * `TARGET_ARCH` - Target architecture (`x86_64` or `i686`)
 * `TEST_INSTALL` - Test running `install` target (`0` or `1`)
 * `UBSAN_BUILD` - Do [UndefinedBehaviourSanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html) build (`0` or `1`)
diff --git a/contrib/ci/scripts/ci_defaults.sh b/contrib/ci/scripts/ci_defaults.sh
index 2fb3fa52a..d8e9376d8 100644
--- a/contrib/ci/scripts/ci_defaults.sh
+++ b/contrib/ci/scripts/ci_defaults.sh
@@ -10,7 +10,7 @@ export JAVA_BINDINGS="${JAVA_BINDINGS:-1}"
 export NO_SUPPRESS_OUTPUT="${NO_SUPPRESS_OUTPUT:-0}"
 export PYTHON_BINDINGS="${PYTHON_BINDINGS:-1}"
 export RUN_SYSTEM_TESTS="${RUN_SYSTEM_TESTS:-1}"
-export RUN_UNIT_TESTS="${RUN_UNIT_TESTS:-1}"
+export RUN_UNIT_TESTS="${RUN_UNIT_TESTS:-BUILD_AND_RUN}"
 export TARGET_ARCH="${TARGET_ARCH:-x86_64}"
 export TEST_INSTALL="${TEST_INSTALL:-1}"
 export UBSAN_BUILD="${UBSAN_BUILD:-0}"
diff --git a/contrib/ci/scripts/test_z3_unit_tests_cmake.sh b/contrib/ci/scripts/test_z3_unit_tests_cmake.sh
index 666673328..e1c927f58 100755
--- a/contrib/ci/scripts/test_z3_unit_tests_cmake.sh
+++ b/contrib/ci/scripts/test_z3_unit_tests_cmake.sh
@@ -10,17 +10,35 @@ set -o pipefail
 : ${Z3_BUILD_DIR?"Z3_BUILD_DIR must be specified"}
 : ${RUN_UNIT_TESTS?"RUN_UNIT_TESTS must be specified"}
 
-if [ "X${RUN_UNIT_TESTS}" != "X1" ]; then
-  echo "Skipping unit tests"
-  exit 0
-fi
-
 # Set CMake generator args
 source ${SCRIPT_DIR}/set_generator_args.sh
 
 cd "${Z3_BUILD_DIR}"
 
-# Build and run internal tests
-cmake --build $(pwd) --target test-z3 "${GENERATOR_ARGS[@]}"
-# Run all tests that don't require arguments
-run_quiet ./test-z3 /a
+function build_unit_tests() {
+  # Build internal tests
+  cmake --build $(pwd) --target test-z3 "${GENERATOR_ARGS[@]}"
+}
+
+function run_unit_tests() {
+  # Run all tests that don't require arguments
+  run_quiet ./test-z3 /a
+}
+
+case "${RUN_UNIT_TESTS}" in
+  BUILD_AND_RUN)
+    build_unit_tests
+    run_unit_tests
+  ;;
+  BUILD_ONLY)
+    build_unit_tests
+  ;;
+  SKIP)
+    echo "RUN_UNIT_TESTS set to \"${RUN_UNIT_TESTS}\" so skipping build and run"
+    exit 0
+  ;;
+  *)
+    echo "Error: RUN_UNIT_TESTS set to unhandled value \"${RUN_UNIT_TESTS}\""
+    exit 1
+  ;;
+esac