diff --git a/.github/workflows/ci-tests.yml b/.github/workflows/ci-tests.yml
index 6b8bcb390..8e4cd2589 100644
--- a/.github/workflows/ci-tests.yml
+++ b/.github/workflows/ci-tests.yml
@@ -157,9 +157,8 @@ jobs:
         # To test the Ant and Gradle builders against each other uncomment the following.
         # (The scripts will use ./gradlew if there is one so we can ensure a specific Gradle version
         # works if that becomes necessary someday.)
-        # FIXME: Do this because this script has been converted from Travis CI to GitHub Actions.
-        ## - tools/compare-gradle-jars-with-ant-jars
-        ## - tools/compare-gradle-tests-with-ant-tests
+        ## tools/compare-gradle-jars-with-ant-jars
+        ## tools/compare-gradle-tests-with-ant-tests
         # Show stdout/stderr so random seeds of failed tests can be obtained by developers to
         # reproduce failed test runs. Also prevents the 10 minute build timeout.
         FREETALK__SHOW_GRADLE_TEST_OUTPUT=1 gradle clean test jar
diff --git a/tools/compare-gradle-jars-with-ant-jars b/tools/compare-gradle-jars-with-ant-jars
index 4735e8228..68ce9d0e3 100755
--- a/tools/compare-gradle-jars-with-ant-jars
+++ b/tools/compare-gradle-jars-with-ant-jars
@@ -4,11 +4,24 @@ set -o errexit
 set -o errtrace
 trap 'echo "Error at line $LINENO, exit code $?" >&2' ERR
 
+case "$OSTYPE" in
+	darwin*)
+		echo "This script does not work on macOS, run it on Linux instead!" >&2
+		echo "(macOS' mktemp does not support the arguments we use.)" >&2
+		exit 1
+		;;
+	msys)
+		echo "This script does not work on MinGW, run it on Linux instead!" >&2
+		echo "(The Ant builder fails on MinGW due to /usr/share/java/junit4.jar not existing.)" >&2
+		exit 1
+		;;
+esac
+
 tmpdir="$(mktemp --directory)"
 trap 'rm -rf -- "$tmpdir"' EXIT
 
 if [ -e "./gradlew" ] ; then
-	# The Travis CI script expects us to use ./gradlew to test compatibility.
+	# The GitHub Actions script  expects us to use ./gradlew to test compatibility.
 	echo "Found ./gradlew, using it instead of system's Gradle."
 	shopt -s expand_aliases
 	unalias -a
diff --git a/tools/compare-gradle-tests-with-ant-tests b/tools/compare-gradle-tests-with-ant-tests
index 3ef5c47b0..948ed22d7 100755
--- a/tools/compare-gradle-tests-with-ant-tests
+++ b/tools/compare-gradle-tests-with-ant-tests
@@ -5,6 +5,19 @@ set -o errexit
 set -o errtrace
 trap 'echo "Error at line $LINENO, exit code $?" >&2' ERR
 
+case "$OSTYPE" in
+	darwin*)
+		echo "This script does not work on macOS, run it on Linux instead!" >&2
+		echo "(macOS' mktemp does not support the arguments we use.)" >&2
+		exit 1
+		;;
+	msys)
+		echo "This script does not work on MinGW, run it on Linux instead!" >&2
+		echo "(The Ant builder fails on MinGW due to /usr/share/java/junit4.jar not existing.)" >&2
+		exit 1
+		;;
+esac
+
 tmpdir="$(mktemp --directory)"
 trap 'rm -rf -- "$tmpdir"' EXIT
 
@@ -12,7 +25,7 @@ from_ant="$(mktemp --tmpdir="$tmpdir" --suffix=.from-ant)"
 from_gradle="$(mktemp --tmpdir="$tmpdir" --suffix=.from-gradle)"
 
 if [ -e "./gradlew" ] ; then
-	# The Travis CI script expects us to use ./gradlew to test compatibility.
+	# The GitHub Actions script expects us to use ./gradlew to test compatibility.
 	echo "Found ./gradlew, using it instead of system's Gradle."
 	shopt -s expand_aliases
 	unalias -a