diff --git a/t/t9390-filter-repo.sh b/t/t9390-filter-repo.sh
index 9017aa9..c7a73bf 100755
--- a/t/t9390-filter-repo.sh
+++ b/t/t9390-filter-repo.sh
@@ -717,4 +717,26 @@ test_expect_success 'startup sanity checks' '
 	)
 '
 
+test_expect_success 'mailmap sanity checks' '
+	(
+		git clone file://"$(pwd)"/analyze_me mailmap_sanity_checks &&
+		cd mailmap_sanity_checks &&
+
+		test_must_fail git filter-repo --mailmap /fake/path 2>../err &&
+		test_i18ngrep "Cannot read /fake/path" ../err &&
+
+		echo "Total Bogus" >../whoopsies &&
+		test_must_fail git filter-repo --mailmap ../whoopsies 2>../err &&
+		test_i18ngrep "Unparseable mailmap file" ../err &&
+		rm ../err &&
+		rm ../whoopsies &&
+
+		echo "Me <me@site.com> Myself <yo@email.com> Extraneous" >../whoopsies &&
+		test_must_fail git filter-repo --mailmap ../whoopsies 2>../err &&
+		test_i18ngrep "Unparseable mailmap file" ../err &&
+		rm ../err &&
+		rm ../whoopsies
+	)
+'
+
 test_done