diff --git a/odb.c b/odb.c
index cf6e7938c0..1d6538163b 100644
--- a/odb.c
+++ b/odb.c
@@ -989,11 +989,33 @@ int odb_write_object_ext(struct object_database *odb,
 			 const void *buf, unsigned long len,
 			 enum object_type type,
 			 struct object_id *oid,
-			 struct object_id *compat_oid,
+			 const struct object_id *compat_oid_in,
 			 enum odb_write_object_flags flags)
 {
+	const struct git_hash_algo *compat = odb->repo->compat_hash_algo;
+	struct object_id compat_oid, *compat_oid_p = NULL;
+
+	if (compat) {
+		const struct git_hash_algo *algo = odb->repo->hash_algo;
+
+		if (compat_oid_in) {
+			oidcpy(&compat_oid, compat_oid_in);
+		} else if (type == OBJ_BLOB) {
+			hash_object_file(compat, buf, len, type, &compat_oid);
+		} else {
+			struct strbuf converted = STRBUF_INIT;
+			convert_object_file(odb->repo, &converted, algo, compat,
+					    buf, len, type, 0);
+			hash_object_file(compat, converted.buf, converted.len,
+					 type, &compat_oid);
+			strbuf_release(&converted);
+		}
+
+		compat_oid_p = &compat_oid;
+	}
+
 	return odb_source_write_object(odb->sources, buf, len, type,
-				       oid, compat_oid, flags);
+				       oid, compat_oid_p, flags);
 }
 
 int odb_write_object_stream(struct object_database *odb,
diff --git a/odb.h b/odb.h
index 94754643d2..066560113e 100644
--- a/odb.h
+++ b/odb.h
@@ -585,9 +585,11 @@ enum odb_write_object_flags {
 
 /*
  * Write an object into the object database. The object is being written into
- * the local alternate of the repository. If provided, the converted object ID
- * as well as the compatibility object ID are written to the respective
- * pointers.
+ * the local alternate of the repository. If provided, the object ID of the
+ * final object is written into `oid`.
+ *
+ * If the caller provides a `compat_oid`, then this compatibility object hash
+ * will be stored instead of computing the compatibility hash ad-hoc.
  *
  * Returns 0 on success, a negative error code otherwise.
  */
@@ -595,7 +597,7 @@ int odb_write_object_ext(struct object_database *odb,
 			 const void *buf, unsigned long len,
 			 enum object_type type,
 			 struct object_id *oid,
-			 struct object_id *compat_oid,
+			 const struct object_id *compat_oid,
 			 enum odb_write_object_flags flags);
 
 static inline int odb_write_object(struct object_database *odb,
diff --git a/odb/source-files.c b/odb/source-files.c
index 4138758511..3d9f5eca32 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -163,7 +163,7 @@ 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,
-					 struct object_id *compat_oid,
+					 const struct object_id *compat_oid,
 					 enum odb_write_object_flags flags)
 {
 	struct odb_source_files *files = odb_source_files_downcast(source);
diff --git a/odb/source-inmemory.c b/odb/source-inmemory.c
index e47bfd8fcc..e727aba427 100644
--- a/odb/source-inmemory.c
+++ b/odb/source-inmemory.c
@@ -231,7 +231,7 @@ 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,
-					    struct object_id *compat_oid UNUSED,
+					    const struct object_id *compat_oid UNUSED,
 					    enum odb_write_object_flags flags UNUSED)
 {
 	struct odb_source_inmemory *inmemory = odb_source_inmemory_downcast(source);
diff --git a/odb/source-loose.c b/odb/source-loose.c
index 3f7d04a56e..ca223109cd 100644
--- a/odb/source-loose.c
+++ b/odb/source-loose.c
@@ -585,32 +585,14 @@ 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,
-					 struct object_id *compat_oid_in,
+					 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;
-	const struct git_hash_algo *compat = source->odb->repo->compat_hash_algo;
-	struct object_id compat_oid;
 	char hdr[MAX_HEADER_LEN];
 	size_t hdrlen = sizeof(hdr);
 
-	/* Generate compat_oid */
-	if (compat) {
-		if (compat_oid_in)
-			oidcpy(&compat_oid, compat_oid_in);
-		else if (type == OBJ_BLOB)
-			hash_object_file(compat, buf, len, type, &compat_oid);
-		else {
-			struct strbuf converted = STRBUF_INIT;
-			convert_object_file(source->odb->repo, &converted, algo, compat,
-					    buf, len, type, 0);
-			hash_object_file(compat, converted.buf, converted.len,
-					 type, &compat_oid);
-			strbuf_release(&converted);
-		}
-	}
-
 	/* Normally if we have it in the pack then we do not bother writing
 	 * it out into .git/objects/??/?{38} file.
 	 */
@@ -619,8 +601,8 @@ static int odb_source_loose_write_object(struct odb_source *source,
 		return 0;
 	if (write_loose_object(loose, oid, hdr, hdrlen, buf, len, 0, flags))
 		return -1;
-	if (compat)
-		return repo_add_loose_object_map(loose, oid, &compat_oid);
+	if (compat_oid)
+		return repo_add_loose_object_map(loose, oid, compat_oid);
 	return 0;
 }
 
diff --git a/odb/source-packed.c b/odb/source-packed.c
index 8d9ce197cc..af0d533375 100644
--- a/odb/source-packed.c
+++ b/odb/source-packed.c
@@ -530,7 +530,7 @@ static int odb_source_packed_write_object(struct odb_source *source UNUSED,
 					  size_t len UNUSED,
 					  enum object_type type UNUSED,
 					  struct object_id *oid UNUSED,
-					  struct object_id *compat_oid UNUSED,
+					  const struct object_id *compat_oid UNUSED,
 					  unsigned flags UNUSED)
 {
 	return error("packed backend cannot write objects");
diff --git a/odb/source.h b/odb/source.h
index cd63dba91f..b3c1ca3a66 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -207,7 +207,7 @@ struct odb_source {
 			    const void *buf, size_t len,
 			    enum object_type type,
 			    struct object_id *oid,
-			    struct object_id *compat_oid,
+			    const struct object_id *compat_oid,
 			    enum odb_write_object_flags flags);
 
 	/*
@@ -417,7 +417,7 @@ 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,
-					  struct object_id *compat_oid,
+					  const struct object_id *compat_oid,
 					  enum odb_write_object_flags flags)
 {
 	return source->write_object(source, buf, len, type, oid,