diff --git a/.github/workflows/build_test.yml b/.github/workflows/build_test.yml
index a7b23d683..ff5e8fd44 100644
--- a/.github/workflows/build_test.yml
+++ b/.github/workflows/build_test.yml
@@ -33,7 +33,7 @@ jobs:
             build_system: cmake
             c_compiler: gcc-9
             cxx_compiler: g++-9
-            os: ubuntu-18.04
+            os: ubuntu-20.04
 
           # TODO: consider running this combination in docker
           #- name: cmake:clang3.5
@@ -114,12 +114,13 @@ jobs:
           # TODO: consider running this combination in docker
           #- name: python2.7:gcc5
 
-          - name: python27:clang9
-            build_system: python
-            c_compiler: clang-9
-            python_version: 2.7
-            cxx_compiler: clang++-9
-            os: ubuntu-18.04
+          # TODO: consider running this combination in docker
+          #- name: python27:clang9
+          #  build_system: python
+          #  c_compiler: clang-9
+          #  python_version: 2.7
+          #  cxx_compiler: clang++-9
+          #  os: ubuntu-20.04
 
           # TODO: consider running this combination in docker
           #- name: python27-win
@@ -202,7 +203,7 @@ jobs:
           - name: bazel-win:root
             build_system: bazel
             bazel_project: .
-            os: windows-latest
+            os: windows-2019
 
           # TODO: use single dll on windows, otherwise it fails to link
           #- name: bazel-win:go
@@ -213,7 +214,7 @@ jobs:
           - name: bazel-win:java
             build_system: bazel
             bazel_project: java
-            os: windows-latest
+            os: windows-2019
 
           # TODO: blocked by Bazel Closure rules issue
           #- name: bazel-win:js
@@ -224,7 +225,7 @@ jobs:
           - name: bazel-win:research
             build_system: bazel
             bazel_project: research
-            os: windows-latest
+            os: windows-2019
 
           - name: make
             build_system: make
@@ -245,7 +246,7 @@ jobs:
     steps:
     - name: Install extra deps @ Ubuntu
       if: ${{ runner.os == 'Linux' }}
-      # Already installed: bazel, clang{10-12}, cmake, gcc{9,10}, java{8,11}, maven, python{2.7,3.5-3.9}
+      # Already installed: bazel, clang{10-12}, cmake, gcc{9,10}, java{8,11}, maven, python{3.5-3.9}
       run: |
         EXTRA_PACKAGES="${{ matrix.extra_apt_pkgs || '' }}"
         sudo apt update
@@ -293,7 +294,7 @@ jobs:
       if: ${{ matrix.build_system == 'bazel' }}
       run: |
         cd ${GITHUB_WORKSPACE}/${{ matrix.bazel_project }}
-        bazel build -c opt ...:all
+        bazelisk build -c opt ...:all
 
     - name: Fix symlinks for Bazel (Windows)
       if: ${{ matrix.build_system == 'bazel' && runner.os == 'Windows' && matrix.bazel_project == 'java' }}
@@ -337,9 +338,9 @@ jobs:
       if: ${{ matrix.build_system == 'bazel' }}
       run: |
         cd ${GITHUB_WORKSPACE}/${{ matrix.bazel_project }}
-        bazel query "tests(...)" --output=label > ${RUNNER_TEMP}/tests.lst
-        [ -s ${RUNNER_TEMP}/tests.lst ] && bazel test -c opt ...:all
-        bazel clean
+        bazelisk query "tests(...)" --output=label > ${RUNNER_TEMP}/tests.lst
+        [ -s ${RUNNER_TEMP}/tests.lst ] && bazelisk test -c opt ...:all
+        bazelisk clean
 
     - name: Build / Test with Maven
       if: ${{ matrix.build_system == 'maven' }}
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9e4cf4083..3c391f604 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,7 +1,7 @@
 # Available CMake versions:
-#  - Ubuntu 18.04 LTS (deprecated on GitHub Actions) : 3.10.4
-#  - Solaris 11.4 SRU 15                             : 3.15 
-cmake_minimum_required(VERSION 3.10.4)
+#  - Ubuntu  20.04 LTS   : 3.16.3
+#  - Solaris 11.4 SRU 15 : 3.15
+cmake_minimum_required(VERSION 3.15)
 
 # Since this project's version is loaded from other files, this policy
 # will help suppress the warning generated by cmake.