diff --git a/t/t4041-diff-submodule-option.sh b/t/t4041-diff-submodule-option.sh
index 306b233e270558..01e1f9be77617e 100755
--- a/t/t4041-diff-submodule-option.sh
+++ b/t/t4041-diff-submodule-option.sh
@@ -13,7 +13,7 @@ This test tries to verify the sanity of the --submodule option of git diff.
 
 # String "added" in German (translated with Google Translate), encoded in UTF-8,
 # used in sample commit log messages in add_file() function below.
-added=$(printf "hinzugef\303\274gt" | iconv -t utf-8)
+added=$(printf "hinzugef\303\274gt")
 add_file () {
 	(
 		cd "$1" &&
@@ -23,8 +23,10 @@ add_file () {
 			echo "$name" >"$name" &&
 			git add "$name" &&
 			test_tick &&
-			msg_added_iso88591=$(echo "Add $name ($added $name)" | iconv -f utf-8 -t iso8859-1) &&
-			git -c 'i18n.commitEncoding=iso8859-1' commit -m "$msg_added_iso88591"
+			# "git commit -m" would break MinGW, as Windows refuse to pass
+			# iso8859-1 encoded parameter to git.
+			echo "Add $name ($added $name)" | iconv -f utf-8 -t iso8859-1 |
+			git -c 'i18n.commitEncoding=iso8859-1' commit -F -
 		done >/dev/null &&
 		git rev-parse --short --verify HEAD
 	)
diff --git a/t/t4205-log-pretty-formats.sh b/t/t4205-log-pretty-formats.sh
index ca532d36d2d61a..f27b0b390af13f 100755
--- a/t/t4205-log-pretty-formats.sh
+++ b/t/t4205-log-pretty-formats.sh
@@ -28,8 +28,9 @@ test_expect_success 'set up basic repos' '
 	git add foo &&
 	test_tick &&
 	git config i18n.commitEncoding iso8859-1 &&
-	commit_msg iso8859-1 > commit_msg &&
-	git commit --file commit_msg &&
+	# "git commit -m" would break MinGW, as Windows refuse to pass
+	# iso8859-1 encoded parameter to git.
+	commit_msg iso8859-1 | git commit -F - &&
 	git add bar &&
 	test_tick &&
 	git commit -m "add bar" &&
diff --git a/t/t7102-reset.sh b/t/t7102-reset.sh
index b05910962b27e3..b5fa177a54b07c 100755
--- a/t/t7102-reset.sh
+++ b/t/t7102-reset.sh
@@ -16,7 +16,7 @@ commit_msg () {
 	msg="modify 2nd file (ge\303\244ndert)\n"
 	if test -n "$1"
 	then
-		printf "$msg" | iconv -t "$1"
+		printf "$msg" | iconv -f utf-8 -t "$1"
 	else
 		printf "$msg"
 	fi
@@ -41,7 +41,9 @@ test_expect_success 'creating initial files and commits' '
 
 	echo "1st line 2nd file" >secondfile &&
 	echo "2nd line 2nd file" >>secondfile &&
-	git -c "i18n.commitEncoding=iso8859-1" commit -a -m "$(commit_msg iso8859-1)" &&
+	# "git commit -m" would break MinGW, as Windows refuse to pass
+	# iso8859-1 encoded parameter to git.
+	commit_msg iso8859-1 | git -c "i18n.commitEncoding=iso8859-1" commit -a -F - &&
 	head5=$(git rev-parse --verify HEAD)
 '
 # git log --pretty=oneline # to see those SHA1 involved
@@ -60,7 +62,7 @@ check_changes () {
 test_expect_success 'reset --hard message' '
 	hex=$(git log -1 --format="%h") &&
 	git reset --hard > .actual &&
-	echo HEAD is now at $hex $(commit_msg utf-8) > .expected &&
+	echo HEAD is now at $hex $(commit_msg) > .expected &&
 	test_cmp .expected .actual
 '
 
@@ -331,7 +333,9 @@ test_expect_success 'redoing the last two commits should succeed' '
 
 	echo "1st line 2nd file" >secondfile &&
 	echo "2nd line 2nd file" >>secondfile &&
-	git -c "i18n.commitEncoding=iso8859-1" commit -a -m "$(commit_msg iso8859-1)" &&
+	# "git commit -m" would break MinGW, as Windows refuse to pass
+	# iso8859-1 encoded parameter to git.
+	commit_msg iso8859-1 | git -c "i18n.commitEncoding=iso8859-1" commit -a -F - &&
 	check_changes $head5
 '