diff --git a/commit.c b/commit.c
index 0ea441d13b..02467676a3 100644
--- a/commit.c
+++ b/commit.c
@@ -9,6 +9,8 @@
 #include "gpg-interface.h"
 #include "mergesort.h"
 
+static struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
+
 int save_commit_buffer = 1;
 
 const char *commit_type = "commit";
@@ -1073,8 +1075,9 @@ static int excluded_header_field(const char *field, size_t len, const char **exc
 	return 0;
 }
 
-struct commit_extra_header *read_commit_extra_header_lines(const char *buffer, size_t size,
-							   const char **exclude)
+static struct commit_extra_header *read_commit_extra_header_lines(
+	const char *buffer, size_t size,
+	const char **exclude)
 {
 	struct commit_extra_header *extra = NULL, **tail = &extra, *it = NULL;
 	const char *line, *next, *eof, *eob;
diff --git a/commit.h b/commit.h
index 6edce87673..9f2131318d 100644
--- a/commit.h
+++ b/commit.h
@@ -204,7 +204,6 @@ extern int commit_tree_extended(const struct strbuf *msg, unsigned char *tree,
 				struct commit_extra_header *);
 
 extern struct commit_extra_header *read_commit_extra_headers(struct commit *, const char **);
-extern struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
 
 extern void free_commit_extra_headers(struct commit_extra_header *extra);