diff --git a/object-file.c b/object-file.c
index 5283292f1e..9ca14f484d 100644
--- a/object-file.c
+++ b/object-file.c
@@ -316,31 +316,6 @@ int parse_loose_header(const char *hdr, struct object_info *oi)
 	return 0;
 }
 
-static void hash_object_body(const struct git_hash_algo *algo, struct git_hash_ctx *c,
-			     const void *buf, size_t len,
-			     struct object_id *oid,
-			     char *hdr, size_t *hdrlen)
-{
-	git_hash_init(c, algo);
-	git_hash_update(c, hdr, *hdrlen);
-	git_hash_update(c, buf, len);
-	git_hash_final_oid(oid, c);
-}
-
-void write_object_file_prepare(const struct git_hash_algo *algo,
-			       const void *buf, size_t len,
-			       enum object_type type, struct object_id *oid,
-			       char *hdr, size_t *hdrlen)
-{
-	struct git_hash_ctx c;
-
-	/* Generate the header */
-	*hdrlen = format_object_header(hdr, *hdrlen, type, len);
-
-	/* Hash (function pointers) computation */
-	hash_object_body(algo, &c, buf, len, oid, hdr, hdrlen);
-}
-
 #define CHECK_COLLISION_DEST_VANISHED -2
 
 static int check_collision(const char *source, const char *dest)
@@ -476,10 +451,16 @@ void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 		      size_t len, enum object_type type,
 		      struct object_id *oid)
 {
+	struct git_hash_ctx c;
 	char hdr[MAX_HEADER_LEN];
-	size_t hdrlen = sizeof(hdr);
+	int hdrlen;
 
-	write_object_file_prepare(algo, buf, len, type, oid, hdr, &hdrlen);
+	hdrlen = format_object_header(hdr, sizeof(hdr), type, len);
+
+	git_hash_init(&c, algo);
+	git_hash_update(&c, hdr, hdrlen);
+	git_hash_update(&c, buf, len);
+	git_hash_final_oid(oid, &c);
 }
 
 struct transaction_packfile {
diff --git a/object-file.h b/object-file.h
index d04ffa6493..08aafcda0d 100644
--- a/object-file.h
+++ b/object-file.h
@@ -134,10 +134,6 @@ int finalize_object_file_flags(struct repository *repo,
 void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 		      size_t len, enum object_type type,
 		      struct object_id *oid);
-void write_object_file_prepare(const struct git_hash_algo *algo,
-			       const void *buf, size_t len,
-			       enum object_type type, struct object_id *oid,
-			       char *hdr, size_t *hdrlen);
 int write_loose_object(struct odb_source_loose *loose,
 		       const struct object_id *oid, char *hdr,
 		       int hdrlen, const void *buf, unsigned long len,
diff --git a/odb.c b/odb.c
index 1d6538163b..4adbdf8a64 100644
--- a/odb.c
+++ b/odb.c
@@ -995,6 +995,8 @@ int odb_write_object_ext(struct object_database *odb,
 	const struct git_hash_algo *compat = odb->repo->compat_hash_algo;
 	struct object_id compat_oid, *compat_oid_p = NULL;
 
+	hash_object_file(odb->repo->hash_algo, buf, len, type, oid);
+
 	if (compat) {
 		const struct git_hash_algo *algo = odb->repo->hash_algo;
 
diff --git a/odb/source-files.c b/odb/source-files.c
index 3d9f5eca32..06dfc8dd78 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -162,7 +162,7 @@ static int odb_source_files_freshen_object(struct odb_source *source,
 static int odb_source_files_write_object(struct odb_source *source,
 					 const void *buf, size_t len,
 					 enum object_type type,
-					 struct object_id *oid,
+					 const struct object_id *oid,
 					 const struct object_id *compat_oid,
 					 enum odb_write_object_flags flags)
 {
diff --git a/odb/source-inmemory.c b/odb/source-inmemory.c
index e727aba427..963d520317 100644
--- a/odb/source-inmemory.c
+++ b/odb/source-inmemory.c
@@ -230,15 +230,13 @@ static int odb_source_inmemory_count_objects(struct odb_source *source,
 static int odb_source_inmemory_write_object(struct odb_source *source,
 					    const void *buf, size_t len,
 					    enum object_type type,
-					    struct object_id *oid,
+					    const struct object_id *oid,
 					    const struct object_id *compat_oid UNUSED,
 					    enum odb_write_object_flags flags UNUSED)
 {
 	struct odb_source_inmemory *inmemory = odb_source_inmemory_downcast(source);
 	struct inmemory_object *object;
 
-	hash_object_file(source->odb->repo->hash_algo, buf, len, type, oid);
-
 	if (!inmemory->objects) {
 		CALLOC_ARRAY(inmemory->objects, 1);
 		oidtree_init(inmemory->objects);
@@ -285,6 +283,8 @@ static int odb_source_inmemory_write_object_stream(struct odb_source *source,
 		goto out;
 	}
 
+	hash_object_file(source->odb->repo->hash_algo, data, total_read, OBJ_BLOB, oid);
+
 	ret = odb_source_inmemory_write_object(source, data, len, OBJ_BLOB, oid,
 					       NULL, 0);
 	if (ret < 0)
diff --git a/odb/source-loose.c b/odb/source-loose.c
index ca223109cd..d4715da6d1 100644
--- a/odb/source-loose.c
+++ b/odb/source-loose.c
@@ -584,19 +584,21 @@ static int odb_source_loose_freshen_object(struct odb_source *source,
 
 static int odb_source_loose_write_object(struct odb_source *source,
 					 const void *buf, size_t len,
-					 enum object_type type, struct object_id *oid,
+					 enum object_type type,
+					 const struct object_id *oid,
 					 const struct object_id *compat_oid,
 					 enum odb_write_object_flags flags)
 {
 	struct odb_source_loose *loose = odb_source_loose_downcast(source);
-	const struct git_hash_algo *algo = source->odb->repo->hash_algo;
 	char hdr[MAX_HEADER_LEN];
-	size_t hdrlen = sizeof(hdr);
+	int hdrlen;
 
-	/* Normally if we have it in the pack then we do not bother writing
+	hdrlen = format_object_header(hdr, sizeof(hdr), type, len);
+
+	/*
+	 * Normally if we have it in the pack then we do not bother writing
 	 * it out into .git/objects/??/?{38} file.
 	 */
-	write_object_file_prepare(algo, buf, len, type, oid, hdr, &hdrlen);
 	if (odb_freshen_object(source->odb, oid))
 		return 0;
 	if (write_loose_object(loose, oid, hdr, hdrlen, buf, len, 0, flags))
diff --git a/odb/source-packed.c b/odb/source-packed.c
index af0d533375..f7f1706447 100644
--- a/odb/source-packed.c
+++ b/odb/source-packed.c
@@ -529,7 +529,7 @@ static int odb_source_packed_write_object(struct odb_source *source UNUSED,
 					  const void *buf UNUSED,
 					  size_t len UNUSED,
 					  enum object_type type UNUSED,
-					  struct object_id *oid UNUSED,
+					  const struct object_id *oid UNUSED,
 					  const struct object_id *compat_oid UNUSED,
 					  unsigned flags UNUSED)
 {
diff --git a/odb/source.h b/odb/source.h
index b3c1ca3a66..c4e94c9d0d 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -206,7 +206,7 @@ struct odb_source {
 	int (*write_object)(struct odb_source *source,
 			    const void *buf, size_t len,
 			    enum object_type type,
-			    struct object_id *oid,
+			    const struct object_id *oid,
 			    const struct object_id *compat_oid,
 			    enum odb_write_object_flags flags);
 
@@ -416,7 +416,7 @@ static inline int odb_source_freshen_object(struct odb_source *source,
 static inline int odb_source_write_object(struct odb_source *source,
 					  const void *buf, unsigned long len,
 					  enum object_type type,
-					  struct object_id *oid,
+					  const struct object_id *oid,
 					  const struct object_id *compat_oid,
 					  enum odb_write_object_flags flags)
 {
diff --git a/t/unit-tests/u-odb-inmemory.c b/t/unit-tests/u-odb-inmemory.c
index 2dbc3ab1df..28a69fc244 100644
--- a/t/unit-tests/u-odb-inmemory.c
+++ b/t/unit-tests/u-odb-inmemory.c
@@ -43,6 +43,7 @@ static void cl_assert_write_object(struct odb_source_inmemory *source,
 				   struct object_id *oid)
 {
 	size_t content_len = strlen(content);
+	hash_object_file(repo.hash_algo, content, content_len, type, oid);
 	cl_must_pass(odb_source_write_object(&source->base, content, content_len,
 					     type, oid, NULL, 0));
 }