diff --git a/.github/workflows/GnuTests.yml b/.github/workflows/GnuTests.yml
index eef8567c7..e901d4cfe 100644
--- a/.github/workflows/GnuTests.yml
+++ b/.github/workflows/GnuTests.yml
@@ -160,34 +160,38 @@ jobs:
     - name: Compare test failures VS reference
       shell: bash
       run: |
+        have_new_failures=""
         REF_LOG_FILE='${{ steps.vars.outputs.path_reference }}/test-logs/test-suite.log'
         REF_SUMMARY_FILE='${{ steps.vars.outputs.path_reference }}/test-summary/gnu-result.json'
         if test -f "${REF_LOG_FILE}"; then
-          echo "Reference SHA1/ID (of '${REF_SUMMARY_FILE}'): $(sha1sum -- "${REF_SUMMARY_FILE}")"
+          echo "Reference SHA1/ID: $(sha1sum -- "${REF_SUMMARY_FILE}")"
           REF_FAILING=$(sed -n "s/^FAIL: \([[:print:]]\+\).*/\1/p" "${REF_LOG_FILE}" | sort)
           NEW_FAILING=$(sed -n "s/^FAIL: \([[:print:]]\+\).*/\1/p" '${{ steps.vars.outputs.path_GNU_tests }}/test-suite.log' | sort)
-          for LINE in $REF_FAILING
+          for LINE in ${REF_FAILING}
           do
-            if ! grep -Fxq $LINE<<<"$NEW_FAILING"; then
-              echo "::warning ::Congrats! The gnu test $LINE is now passing!"
+            if ! grep -Fxq ${LINE}<<<"${NEW_FAILING}"; then
+              echo "::warning ::Congrats! The gnu test ${LINE} is now passing!"
             fi
           done
-          for LINE in $NEW_FAILING
+          for LINE in ${NEW_FAILING}
           do
-            if ! grep -Fxq $LINE<<<"$REF_FAILING"
+            if ! grep -Fxq ${LINE}<<<"${REF_FAILING}"
             then
-              echo "::error ::GNU test failed: $LINE. $LINE is passing on '${{ steps.vars.outputs.repo_default_branch }}'. Maybe you have to rebase?"
+              echo "::error ::GNU test failed: ${LINE}. ${LINE} is passing on '${{ steps.vars.outputs.repo_default_branch }}'. Maybe you have to rebase?"
+              have_new_failures="true"
             fi
           done
         else
           echo "::warning ::Skipping test failure comparison; no prior reference test logs are available."
         fi
+        if test -n "${have_new_failures}" ; then exit -1 ; fi
     - name: Compare test summary VS reference
+      if: success() || failure() # run regardless of prior step success/failure
       shell: bash
       run: |
         REF_SUMMARY_FILE='${{ steps.vars.outputs.path_reference }}/test-summary/gnu-result.json'
         if test -f "${REF_SUMMARY_FILE}"; then
-          echo "Reference SHA1/ID (of '${REF_SUMMARY_FILE}'): $(sha1sum -- "${REF_SUMMARY_FILE}")"
+          echo "Reference SHA1/ID: $(sha1sum -- "${REF_SUMMARY_FILE}")"
           mv "${REF_SUMMARY_FILE}" main-gnu-result.json
           python uutils/util/compare_gnu_result.py
         else
diff --git a/util/build-gnu.sh b/util/build-gnu.sh
index 2ab23ddc7..bb8d6e522 100755
--- a/util/build-gnu.sh
+++ b/util/build-gnu.sh
@@ -70,19 +70,38 @@ sed -i 's|^"\$@|/usr/bin/timeout 600 "\$@|' build-aux/test-driver
 sed -i "s/^[[:blank:]]*PATH=.*/  PATH='${UU_BUILD_DIR//\//\\/}\$(PATH_SEPARATOR)'\"\$\$PATH\" \\\/" Makefile
 sed -i 's| tr | /usr/bin/tr |' tests/init.sh
 make -j "$(nproc)"
-# Generate the factor tests, so they can be fixed
-# Used to be 36. Reduced to 20 to decrease the log size
-for i in {00..20}; do
-    make "tests/factor/t${i}.sh"
-done
-
-# strip the long stuff
-for i in {21..36}; do
+first=00
+if test ${UU_MAKE_PROFILE} != "debug"; then
+    # Generate the factor tests, so they can be fixed
+    # * reduced to 20 to decrease log size (down from 36 expected by GNU)
+    # * only for 'release', skipped for 'debug' as redundant and too time consuming (causing timeout errors)
+    seq=$(
+        i=${first}
+        while test "$i" -le 20; do
+            printf '%02d ' $i
+            i=$(($i + 1))
+        done
+    )
+    for i in ${seq}; do
+        make "tests/factor/t${i}.sh"
+    done
+    sed -i -e 's|^seq |/usr/bin/seq |' -e 's|sha1sum |/usr/bin/sha1sum |' tests/factor/t*sh
+    first=21
+fi
+# strip all (debug) or just the longer (release) factor tests from Makefile
+seq=$(
+    i=${first}
+    while test "$i" -le 36; do
+        printf '%02d ' $i
+        i=$(($i + 1))
+    done
+)
+for i in ${seq}; do
+    echo "strip t${i}.sh from Makefile"
     sed -i -e "s/\$(tf)\/t${i}.sh//g" Makefile
 done
 
 grep -rl 'path_prepend_' tests/* | xargs sed -i 's| path_prepend_ ./src||'
-sed -i -e 's|^seq |/usr/bin/seq |' -e 's|sha1sum |/usr/bin/sha1sum |' tests/factor/t*sh
 
 # Remove tests checking for --version & --help
 # Not really interesting for us and logs are too big