diff --git a/commit.h b/commit.h
index f4fc5c5589..95f981a1a9 100644
--- a/commit.h
+++ b/commit.h
@@ -70,7 +70,7 @@ extern char *reencode_commit_message(const struct commit *commit,
 				     const char **encoding_p);
 extern void get_commit_format(const char *arg, struct rev_info *);
 extern void format_commit_message(const struct commit *commit,
-				  const void *format, struct strbuf *sb,
+				  const char *format, struct strbuf *sb,
 				  enum date_mode dmode);
 extern void pretty_print_commit(enum cmit_fmt fmt, const struct commit*,
                                 struct strbuf *,
diff --git a/pretty.c b/pretty.c
index f5983f8baa..587101f846 100644
--- a/pretty.c
+++ b/pretty.c
@@ -740,7 +740,7 @@ static size_t format_commit_item(struct strbuf *sb, const char *placeholder,
 }
 
 void format_commit_message(const struct commit *commit,
-			   const void *format, struct strbuf *sb,
+			   const char *format, struct strbuf *sb,
 			   enum date_mode dmode)
 {
 	struct format_commit_context context;