diff --git a/.circleci/config.yml b/.circleci/config.yml
index 11ca1d7a8..c90ef4c4c 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -7,7 +7,8 @@ jobs:
       - image: ubuntu:17.10
     steps:
       - checkout
-      - run: apt update && apt install -y ninja-build binutils libtool autoconf automake make cmake gcc g++ pkg-config ragel gtk-doc-tools libfreetype6-dev libglib2.0-dev libcairo2-dev libicu-dev libgraphite2-dev
+      - run: apt update && apt install -y ninja-build binutils libtool autoconf automake make cmake gcc g++ pkg-config ragel gtk-doc-tools libfreetype6-dev libglib2.0-dev libcairo2-dev libicu-dev libgraphite2-dev python python-pip
+      - run: pip install fonttools
       - run: ./autogen.sh && make distcheck && rm -rf harfbuzz-*
       - run: make distdir && cd harfbuzz-* && cmake -DHB_CHECK=ON -Bbuild -H. -GNinja && ninja -Cbuild && CTEST_OUTPUT_ON_FAILURE=1 ninja -Cbuild test && ninja -Cbuild install
 
@@ -43,7 +44,8 @@ jobs:
       - image: ubuntu:17.10
     steps:
       - checkout
-      - run: apt update && apt install -y ninja-build binutils cmake gcc g++ pkg-config ragel gtk-doc-tools libfreetype6-dev libglib2.0-dev libcairo2-dev libicu-dev libgraphite2-dev
+      - run: apt update && apt install -y ninja-build binutils cmake gcc g++ pkg-config ragel gtk-doc-tools libfreetype6-dev libglib2.0-dev libcairo2-dev libicu-dev libgraphite2-dev python python-pip
+      - run: pip install fonttools
       - run: cmake -DHB_CHECK=ON -Bbuild -H. -GNinja
       - run: ninja -Cbuild
       - run: CTEST_OUTPUT_ON_FAILURE=1 ninja -Cbuild test
diff --git a/test/subset/CMakeLists.txt b/test/subset/CMakeLists.txt
index 6fe377e14..ea04105c0 100644
--- a/test/subset/CMakeLists.txt
+++ b/test/subset/CMakeLists.txt
@@ -2,9 +2,9 @@ if (HB_BUILD_UTILS)
   file (READ "${CMAKE_CURRENT_SOURCE_DIR}/data/Makefile.sources" SOURCES)
   extract_make_variable (TESTS ${SOURCES})
   foreach (test IN ITEMS ${TESTS})
-# TODO(grieger): Re-enable once ttx is available in CI environments.
-#    add_test (NAME ${test}
-#      COMMAND python run-tests.py $<TARGET_FILE:hb-subset> "data/${test}"
-#      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+    add_test (NAME ${test}
+      COMMAND python run-tests.py $<TARGET_FILE:hb-subset> "data/${test}"
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+    set_property(TEST ${test} PROPERTY SKIP_RETURN_CODE 77)
   endforeach ()
 endif ()