diff --git a/.github/workflows/cmake_nagfor.yml b/.github/workflows/cmake_nagfor.yml
index 12d9fe8856..feaab56694 100644
--- a/.github/workflows/cmake_nagfor.yml
+++ b/.github/workflows/cmake_nagfor.yml
@@ -16,9 +16,6 @@ on:
       stress-test:
         description: Stress Test (Optional, true or false)
         required: false
-      cflags:
-        description: CFLAGS
-        required: false
       fflags:
         description: FFLAGS
         required: false
@@ -56,11 +53,17 @@ jobs:
       - name: Conduct the test
         run: |
           source ~/local/bin/nag_licensing || echo "\n\nNAG licensing failed.\n\n"
+          export CFLAGS="-Wall -Wextra -Wpedantic -Werror"
           export FC=nagfor
-          #export FFLAGS='-fpp -nan -ieee=stop -recursive -info -gline -u -C -C=alias -C=dangling -C=intovf -C=undefined -kind=unique -Warn=constant_coindexing -Warn=subnormal'
-          #export CFLAGS='-Wall -Wextra -Wpedantic -Werror'
-          export FFLAGS="${{ github.event.inputs.fflags }}"
-          export CFLAGS="${{ github.event.inputs.cflags }}"
+          if [[ -n "${{ github.event.inputs.fflags }}" ]]; then
+              export FFLAGS="${{ github.event.inputs.fflags }}"
+          else
+              export FFLAGS='-fpp -nan -ieee=stop -recursive -info -gline -u -C -C=alias -C=dangling -C=intovf -kind=unique -Warn=constant_coindexing -Warn=subnormal'
+              # Zaikun 20240121: With gcc 11.4.0 and nagfor 7.1.7143, if '-C=undefined' is included
+              # in FFLAGS, then the C tests will encounter a segmentation fault, although the Fortran
+              # tests work correctly.
+              #export FFLAGS='-fpp -nan -ieee=stop -recursive -info -gline -u -C -C=alias -C=dangling -C=intovf -C=undefined -kind=unique -Warn=constant_coindexing -Warn=subnormal'
+          fi
           cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=. -LAH -DCMAKE_C_FLAGS="${CFLAGS}" -DCMAKE_Fortran_FLAGS="${FFLAGS}" .
           cmake --build . --target install
           cmake --build . --target tests