diff --git a/Documentation/git-format-patch.txt b/Documentation/git-format-patch.txt
index 728bb3821c..e553810b1e 100644
--- a/Documentation/git-format-patch.txt
+++ b/Documentation/git-format-patch.txt
@@ -20,7 +20,7 @@ SYNOPSIS
 		   [--in-reply-to=<message-id>] [--suffix=.<sfx>]
 		   [--ignore-if-in-upstream] [--always]
 		   [--cover-from-description=<mode>]
-		   [--rfc] [--subject-prefix=<subject-prefix>]
+		   [--rfc[=<rfc>]] [--subject-prefix=<subject-prefix>]
 		   [(--reroll-count|-v) <n>]
 		   [--to=<email>] [--cc=<email>]
 		   [--[no-]cover-letter] [--quiet]
@@ -238,10 +238,15 @@ the patches (with a value of e.g. "PATCH my-project").
 	value of the `format.filenameMaxLength` configuration
 	variable, or 64 if unconfigured.
 
---rfc::
-	Prepends "RFC" to the subject prefix (producing "RFC PATCH" by
-	default). RFC means "Request For Comments"; use this when sending
-	an experimental patch for discussion rather than application.
+--rfc[=<rfc>]::
+	Prepends the string _<rfc>_ (defaults to "RFC") to
+	the subject prefix.  As the subject prefix defaults to
+	"PATCH", you'll get "RFC PATCH" by default.
++
+RFC means "Request For Comments"; use this when sending
+an experimental patch for discussion rather than application.
+"--rfc=WIP" may also be a useful way to indicate that a patch
+is not complete yet ("WIP" stands for "Work In Progress").
 
 -v <n>::
 --reroll-count=<n>::
diff --git a/builtin/log.c b/builtin/log.c
index c0a8bb95e9..97ca885b33 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1494,6 +1494,19 @@ static int subject_prefix_callback(const struct option *opt, const char *arg,
 	return 0;
 }
 
+static int rfc_callback(const struct option *opt, const char *arg,
+			int unset)
+{
+	const char **rfc = opt->value;
+
+	*rfc = opt->value;
+	if (unset)
+		*rfc = NULL;
+	else
+		*rfc = arg ? arg : "RFC";
+	return 0;
+}
+
 static int numbered_cmdline_opt = 0;
 
 static int numbered_callback(const struct option *opt, const char *arg,
@@ -1907,8 +1920,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	struct strbuf rdiff2 = STRBUF_INIT;
 	struct strbuf rdiff_title = STRBUF_INIT;
 	struct strbuf sprefix = STRBUF_INIT;
+	const char *rfc = NULL;
 	int creation_factor = -1;
-	int rfc = 0;
 
 	const struct option builtin_format_patch_options[] = {
 		OPT_CALLBACK_F('n', "numbered", &numbered, NULL,
@@ -1932,7 +1945,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    N_("mark the series as Nth re-roll")),
 		OPT_INTEGER(0, "filename-max-length", &fmt_patch_name_max,
 			    N_("max length of output filename")),
-		OPT_BOOL(0, "rfc", &rfc, N_("use [RFC PATCH] instead of [PATCH]")),
+		OPT_CALLBACK_F(0, "rfc", &rfc, N_("rfc"),
+			       N_("add <rfc> (default 'RFC') before 'PATCH'"),
+			       PARSE_OPT_OPTARG, rfc_callback),
 		OPT_STRING(0, "cover-from-description", &cover_from_description_arg,
 			    N_("cover-from-description-mode"),
 			    N_("generate parts of a cover letter based on a branch's description")),
@@ -2050,8 +2065,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (cover_from_description_arg)
 		cover_from_description_mode = parse_cover_from_description(cover_from_description_arg);
 
-	if (rfc)
-		strbuf_insertstr(&sprefix, 0, "RFC ");
+	if (rfc && rfc[0])
+		strbuf_insertf(&sprefix, 0, "%s ", rfc);
 
 	if (reroll_count) {
 		strbuf_addf(&sprefix, " v%s", reroll_count);
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index e37a1411ee..645c4189f9 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1368,13 +1368,30 @@ test_expect_success 'empty subject prefix does not have extra space' '
 	test_cmp expect actual
 '
 
-test_expect_success '--rfc' '
+test_expect_success '--rfc and --no-rfc' '
 	cat >expect <<-\EOF &&
 	Subject: [RFC PATCH 1/1] header with . in it
 	EOF
 	git format-patch -n -1 --stdout --rfc >patch &&
 	grep "^Subject:" patch >actual &&
-	test_cmp expect actual
+	test_cmp expect actual &&
+	git format-patch -n -1 --stdout --rfc --no-rfc >patch &&
+	sed -e "s/RFC //" expect >expect-raw &&
+	grep "^Subject:" patch >actual &&
+	test_cmp expect-raw actual
+'
+
+test_expect_success '--rfc=WIP and --rfc=' '
+	cat >expect <<-\EOF &&
+	Subject: [WIP PATCH 1/1] header with . in it
+	EOF
+	git format-patch -n -1 --stdout --rfc=WIP >patch &&
+	grep "^Subject:" patch >actual &&
+	test_cmp expect actual &&
+	git format-patch -n -1 --stdout --rfc --rfc= >patch &&
+	sed -e "s/WIP //" expect >expect-raw &&
+	grep "^Subject:" patch >actual &&
+	test_cmp expect-raw actual
 '
 
 test_expect_success '--rfc does not overwrite prefix' '