diff --git a/.github/workflows/cmake.yml b/.github/workflows/cmake.yml
index a6d892076b..a9e138717d 100644
--- a/.github/workflows/cmake.yml
+++ b/.github/workflows/cmake.yml
@@ -26,6 +26,9 @@ permissions:
 
 jobs:
 
+  # N.B.: It is tempting to use environment variables to define the compiler flags to avoid
+  # repeating them, but this is not supported as of 20240501. See
+  # https://stackoverflow.com/questions/74072206/github-actions-use-variables-in-matrix-definition
   cmake-main:
     runs-on: ${{ matrix.os }}
     continue-on-error: true
@@ -148,7 +151,7 @@ jobs:
           cmake --version
 
           VERBOSE_MAKEFILE=OFF
-          if [[ ${{ github.event.inputs.verbose-makefile }} == 'true' ]] ; then
+          if [[ "${{ github.event.inputs.verbose-makefile }}" == "true" ]] ; then
               VERBOSE_MAKEFILE=ON
           fi
 
diff --git a/.github/workflows/cmake_mac.yml b/.github/workflows/cmake_mac.yml
index 8c887f5397..7bcac6a138 100644
--- a/.github/workflows/cmake_mac.yml
+++ b/.github/workflows/cmake_mac.yml
@@ -79,7 +79,7 @@ jobs:
           cmake --version
 
           VERBOSE_MAKEFILE=OFF
-          if [[ ${{ github.event.inputs.verbose-makefile }} == 'true' ]] ; then
+          if [[ "${{ github.event.inputs.verbose-makefile }}" == "true" ]] ; then
               VERBOSE_MAKEFILE=ON
           fi
 
diff --git a/.github/workflows/cmake_mac_nagfor.yml b/.github/workflows/cmake_mac_nagfor.yml
index fb353e9421..7cf639cbf9 100644
--- a/.github/workflows/cmake_mac_nagfor.yml
+++ b/.github/workflows/cmake_mac_nagfor.yml
@@ -79,7 +79,7 @@ jobs:
           cmake --version
 
           VERBOSE_MAKEFILE=OFF
-          if [[ ${{ github.event.inputs.verbose-makefile }} == 'true' ]] ; then
+          if [[ "${{ github.event.inputs.verbose-makefile }}" == "true" ]] ; then
               VERBOSE_MAKEFILE=ON
           fi
 
diff --git a/.github/workflows/cmake_nagfor.yml b/.github/workflows/cmake_nagfor.yml
index 6be31be203..bd45b740f6 100644
--- a/.github/workflows/cmake_nagfor.yml
+++ b/.github/workflows/cmake_nagfor.yml
@@ -76,7 +76,7 @@ jobs:
           cmake --version
 
           VERBOSE_MAKEFILE=OFF
-          if [[ ${{ github.event.inputs.verbose-makefile }} == 'true' ]] ; then
+          if [[ "${{ github.event.inputs.verbose-makefile }}" == "true" ]] ; then
               VERBOSE_MAKEFILE=ON
           fi
 
diff --git a/.github/workflows/cmake_pi.yml b/.github/workflows/cmake_pi.yml
index 23c268fbd7..42b5f3eee4 100644
--- a/.github/workflows/cmake_pi.yml
+++ b/.github/workflows/cmake_pi.yml
@@ -74,7 +74,7 @@ jobs:
           cmake --version
 
           VERBOSE_MAKEFILE=OFF
-          if [[ ${{ github.event.inputs.verbose-makefile }} == 'true' ]] ; then
+          if [[ "${{ github.event.inputs.verbose-makefile }}" == "true" ]] ; then
               VERBOSE_MAKEFILE=ON
           fi