diff --git a/t/t1300-repo-config.sh b/t/t1300-repo-config.sh
index 187ca2df5c81245256630428d3fc47567e0b4112..1d2bf2c06087546503b7272a9547ab8232b017d4 100755
--- a/t/t1300-repo-config.sh
+++ b/t/t1300-repo-config.sh
@@ -325,6 +325,9 @@ EOF
 
 test_expect_success 'new variable inserts into proper section' 'cmp .git/config expect'
 
+test_expect_success 'alternative GIT_CONFIG (non-existing file should fail)' \
+	'git config --file non-existing-config -l; test $? != 0'
+
 cat > other-config << EOF
 [ein]
 	bahn = strasse
@@ -338,6 +341,9 @@ GIT_CONFIG=other-config git config -l > output
 
 test_expect_success 'alternative GIT_CONFIG' 'cmp output expect'
 
+test_expect_success 'alternative GIT_CONFIG (--file)' \
+	'git config --file other-config -l > output && cmp output expect'
+
 GIT_CONFIG=other-config git config anwohner.park ausweis
 
 cat > expect << EOF