diff --git a/commit.c b/commit.c
index bee066f..5632e32 100644
--- a/commit.c
+++ b/commit.c
@@ -511,12 +511,16 @@
 	bp += i;
 	for (i = 0; i < len; i++) {
 		unsigned ch = line[i] & 0xFF;
-		if (is_rfc2047_special(ch)) {
+		/*
+		 * We encode ' ' using '=20' even though rfc2047
+		 * allows using '_' for readability.  Unfortunately,
+		 * many programs do not understand this and just
+		 * leave the underscore in place.
+		 */
+		if (is_rfc2047_special(ch) || ch == ' ') {
 			sprintf(bp, "=%02X", ch);
 			bp += 3;
 		}
-		else if (ch == ' ')
-			*bp++ = '_';
 		else
 			*bp++ = ch;
 	}
diff --git a/t/t3901-i18n-patch.sh b/t/t3901-i18n-patch.sh
index a881797..24bf0ee 100755
--- a/t/t3901-i18n-patch.sh
+++ b/t/t3901-i18n-patch.sh
@@ -13,7 +13,7 @@
 	while test "$i" -le $cnt
 	do
 		git format-patch --encoding=UTF-8 --stdout HEAD~$i..HEAD~$j |
-		grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD_=C3=B3=C3=BA?=" &&
+		grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD=20=C3=B3=C3=BA?=" &&
 		git-cat-file commit HEAD~$j |
 		case "$header" in
 		8859)
@@ -73,9 +73,9 @@
 	git format-patch --stdout master..HEAD^ >out-l1 &&
 	git format-patch --stdout HEAD^ >out-l2 &&
 	grep "^Content-Type: text/plain; charset=ISO-8859-1" out-l1 &&
-	grep "^From: =?ISO-8859-1?q?=C1=E9=ED_=F3=FA?=" out-l1 &&
+	grep "^From: =?ISO-8859-1?q?=C1=E9=ED=20=F3=FA?=" out-l1 &&
 	grep "^Content-Type: text/plain; charset=ISO-8859-1" out-l2 &&
-	grep "^From: =?ISO-8859-1?q?=C1=E9=ED_=F3=FA?=" out-l2
+	grep "^From: =?ISO-8859-1?q?=C1=E9=ED=20=F3=FA?=" out-l2
 '
 
 test_expect_success 'format-patch output (UTF-8)' '
@@ -84,9 +84,9 @@
 	git format-patch --stdout master..HEAD^ >out-u1 &&
 	git format-patch --stdout HEAD^ >out-u2 &&
 	grep "^Content-Type: text/plain; charset=UTF-8" out-u1 &&
-	grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD_=C3=B3=C3=BA?=" out-u1 &&
+	grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD=20=C3=B3=C3=BA?=" out-u1 &&
 	grep "^Content-Type: text/plain; charset=UTF-8" out-u2 &&
-	grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD_=C3=B3=C3=BA?=" out-u2
+	grep "^From: =?UTF-8?q?=C3=81=C3=A9=C3=AD=20=C3=B3=C3=BA?=" out-u2
 '
 
 test_expect_success 'rebase (U/U)' '