diff --git a/revision.c b/revision.c
index 07412297f0..2eb9ff089b 100644
--- a/revision.c
+++ b/revision.c
@@ -3934,7 +3934,7 @@ struct commit *get_revision(struct rev_info *revs)
 	return c;
 }
 
-char *get_revision_mark(const struct rev_info *revs, const struct commit *commit)
+const char *get_revision_mark(const struct rev_info *revs, const struct commit *commit)
 {
 	if (commit->object.flags & BOUNDARY)
 		return "-";
@@ -3956,7 +3956,7 @@ char *get_revision_mark(const struct rev_info *revs, const struct commit *commit
 
 void put_revision_mark(const struct rev_info *revs, const struct commit *commit)
 {
-	char *mark = get_revision_mark(revs, commit);
+	const char *mark = get_revision_mark(revs, commit);
 	if (!strlen(mark))
 		return;
 	fputs(mark, stdout);
diff --git a/revision.h b/revision.h
index 4134dc6029..addd69410b 100644
--- a/revision.h
+++ b/revision.h
@@ -322,8 +322,8 @@ int handle_revision_arg(const char *arg, struct rev_info *revs,
 void reset_revision_walk(void);
 int prepare_revision_walk(struct rev_info *revs);
 struct commit *get_revision(struct rev_info *revs);
-char *get_revision_mark(const struct rev_info *revs,
-			const struct commit *commit);
+const char *get_revision_mark(const struct rev_info *revs,
+			      const struct commit *commit);
 void put_revision_mark(const struct rev_info *revs,
 		       const struct commit *commit);