diff --git a/.github/workflows/test_eessi.yml b/.github/workflows/test_eessi.yml
index 92b1f71cad..04195dd619 100644
--- a/.github/workflows/test_eessi.yml
+++ b/.github/workflows/test_eessi.yml
@@ -40,4 +40,33 @@ jobs:
               export EESSI_OS_TYPE=linux
               export EESSI_SOFTWARE_SUBDIR=${{matrix.EESSI_SOFTWARE_SUBDIR}}
               env | grep ^EESSI | sort
+              echo "just run check_missing_installations.sh (should use eessi-${{matrix.EESSI_VERSION}}.yml)"
               ./check_missing_installations.sh
+
+        - name: Test check_missing_installations.sh with missing package (GCC/8.3.0)
+          run: |
+              source /cvmfs/pilot.eessi-hpc.org/versions/${{matrix.EESSI_VERSION}}/init/bash
+              module load EasyBuild
+              eb --version
+              export EESSI_PREFIX=/cvmfs/pilot.eessi-hpc.org/versions/${{matrix.EESSI_VERSION}}
+              export EESSI_OS_TYPE=linux
+              export EESSI_SOFTWARE_SUBDIR=${{matrix.EESSI_SOFTWARE_SUBDIR}}
+              env | grep ^EESSI | sort
+              echo "modify eessi-${{matrix.EESSI_VERSION}}.yml by adding a missing package (GCC/8.3.0)"
+              echo "  GCC:" >> eessi-${{matrix.EESSI_VERSION}}.yml
+              echo "    toolchains:" >> eessi-${{matrix.EESSI_VERSION}}.yml
+              echo "      SYSTEM:" >> eessi-${{matrix.EESSI_VERSION}}.yml
+              echo "        versions: '8.3.0'" >> eessi-${{matrix.EESSI_VERSION}}.yml
+              tail -n 4 eessi-${{matrix.EESSI_VERSION}}.yml
+              # note, check_missing_installations.sh exits 1 if a package was
+              # missing, which is intepreted as false (exit code based, not
+              # boolean logic), hence when the script exits 0 if no package was
+              # missing it is interpreted as true, thus the test did not capture
+              # the missing package
+              if ./check_missing_installations.sh; then
+                echo "did NOT capture missing package; test FAILED"
+                exit 1
+              else
+                echo "captured missing package; test PASSED"
+                exit 0
+              fi
diff --git a/check_missing_installations.sh b/check_missing_installations.sh
index e4c75aebd8..926f475903 100755
--- a/check_missing_installations.sh
+++ b/check_missing_installations.sh
@@ -27,5 +27,18 @@ eb_missing_out=$LOCAL_TMPDIR/eb_missing.out
 # we need to use --from-pr to pull in some easyconfigs that are not available in EasyBuild version being used
 # PR #16531: Nextflow-22.10.1.eb
 ${EB:-eb} --from-pr 16531 --easystack eessi-${EESSI_PILOT_VERSION}.yml --experimental --missing | tee ${eb_missing_out}
-grep "No missing modules" ${eb_missing_out} > /dev/null
-check_exit_code $? "${ok_msg}" "${fail_msg}"
+
+# the above assesses the installed software for each easyconfig provided in
+# the easystack file and then print messages such as
+# `No missing modules!`
+# or
+# `2 out of 3 required modules missing:`
+# depending on the result of the assessment. Hence, we need to check if the
+# output does not contain any line with ` required modules missing:`
+
+grep " required modules missing:" ${eb_missing_out} > /dev/null
+
+# if grep returns 1 (` required modules missing:` was NOT found), we set
+# MODULES_MISSING to 0, otherwise (it was found or another error) we set it to 1
+[[ $? -eq 1 ]] && MODULES_MISSING=0 || MODULES_MISSING=1
+check_exit_code ${MODULES_MISSING} "${ok_msg}" "${fail_msg}"