diff --git a/builtin/checkout.c b/builtin/checkout.c
index 8eb118201d..5981e1a3ed 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -720,7 +720,7 @@ static int add_pending_uninteresting_ref(const char *refname,
 static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
 {
 	strbuf_addstr(sb, "  ");
-	strbuf_add_unique_abbrev(sb, commit->object.oid.hash, DEFAULT_ABBREV);
+	strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
 	strbuf_addch(sb, ' ');
 	if (!parse_commit(commit))
 		pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
diff --git a/builtin/fetch.c b/builtin/fetch.c
index d32d94692c..aeafe63ba6 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -708,9 +708,9 @@ static int update_local_ref(struct ref *ref,
 	if (in_merge_bases(current, updated)) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
-		strbuf_add_unique_abbrev(&quickref, current->object.oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
-		strbuf_add_unique_abbrev(&quickref, ref->new_oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
 		if ((recurse_submodules != RECURSE_SUBMODULES_OFF) &&
 		    (recurse_submodules != RECURSE_SUBMODULES_ON))
 			check_for_new_submodule_commits(&ref->new_oid);
@@ -723,9 +723,9 @@ static int update_local_ref(struct ref *ref,
 	} else if (force || ref->force) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
-		strbuf_add_unique_abbrev(&quickref, current->object.oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "...");
-		strbuf_add_unique_abbrev(&quickref, ref->new_oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
 		if ((recurse_submodules != RECURSE_SUBMODULES_OFF) &&
 		    (recurse_submodules != RECURSE_SUBMODULES_ON))
 			check_for_new_submodule_commits(&ref->new_oid);
diff --git a/builtin/tag.c b/builtin/tag.c
index 8c493a569f..a5fc6c090f 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -293,7 +293,7 @@ static void create_reflog_msg(const struct object_id *oid, struct strbuf *sb)
 		strbuf_addstr(sb, rla);
 	} else {
 		strbuf_addstr(sb, "tag: tagging ");
-		strbuf_add_unique_abbrev(sb, oid->hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(sb, oid, DEFAULT_ABBREV);
 	}
 
 	strbuf_addstr(sb, " (");
diff --git a/merge-recursive.c b/merge-recursive.c
index c886f2e9cd..f58f13957e 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -228,7 +228,7 @@ static void output_commit_title(struct merge_options *o, struct commit *commit)
 		strbuf_addf(&o->obuf, "virtual %s\n",
 			merge_remote_util(commit)->name);
 	else {
-		strbuf_add_unique_abbrev(&o->obuf, commit->object.oid.hash,
+		strbuf_add_unique_abbrev(&o->obuf, &commit->object.oid,
 					 DEFAULT_ABBREV);
 		strbuf_addch(&o->obuf, ' ');
 		if (parse_commit(commit) != 0)
diff --git a/pretty.c b/pretty.c
index f7ce490230..34fe891fc0 100644
--- a/pretty.c
+++ b/pretty.c
@@ -549,7 +549,7 @@ static void add_merge_info(const struct pretty_print_context *pp,
 		struct object_id *oidp = &parent->item->object.oid;
 		strbuf_addch(sb, ' ');
 		if (pp->abbrev)
-			strbuf_add_unique_abbrev(sb, oidp->hash, pp->abbrev);
+			strbuf_add_unique_abbrev(sb, oidp, pp->abbrev);
 		else
 			strbuf_addstr(sb, oid_to_hex(oidp));
 		parent = parent->next;
@@ -1156,7 +1156,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		return 1;
 	case 'h':		/* abbreviated commit hash */
 		strbuf_addstr(sb, diff_get_color(c->auto_color, DIFF_COMMIT));
-		strbuf_add_unique_abbrev(sb, commit->object.oid.hash,
+		strbuf_add_unique_abbrev(sb, &commit->object.oid,
 					 c->pretty_ctx->abbrev);
 		strbuf_addstr(sb, diff_get_color(c->auto_color, DIFF_RESET));
 		return 1;
@@ -1164,7 +1164,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		strbuf_addstr(sb, oid_to_hex(&commit->tree->object.oid));
 		return 1;
 	case 't':		/* abbreviated tree hash */
-		strbuf_add_unique_abbrev(sb, commit->tree->object.oid.hash,
+		strbuf_add_unique_abbrev(sb, &commit->tree->object.oid,
 					 c->pretty_ctx->abbrev);
 		return 1;
 	case 'P':		/* parent hashes */
@@ -1178,7 +1178,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		for (p = commit->parents; p; p = p->next) {
 			if (p != commit->parents)
 				strbuf_addch(sb, ' ');
-			strbuf_add_unique_abbrev(sb, p->item->object.oid.hash,
+			strbuf_add_unique_abbrev(sb, &p->item->object.oid,
 						 c->pretty_ctx->abbrev);
 		}
 		return 1;
diff --git a/strbuf.c b/strbuf.c
index 5f138ed3c8..07309045ef 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -873,12 +873,12 @@ void strbuf_addftime(struct strbuf *sb, const char *fmt, const struct tm *tm,
 	strbuf_setlen(sb, sb->len + len);
 }
 
-void strbuf_add_unique_abbrev(struct strbuf *sb, const unsigned char *sha1,
+void strbuf_add_unique_abbrev(struct strbuf *sb, const struct object_id *oid,
 			      int abbrev_len)
 {
 	int r;
 	strbuf_grow(sb, GIT_SHA1_HEXSZ + 1);
-	r = find_unique_abbrev_r(sb->buf + sb->len, sha1, abbrev_len);
+	r = find_unique_abbrev_r(sb->buf + sb->len, oid->hash, abbrev_len);
 	strbuf_setlen(sb, sb->len + r);
 }
 
diff --git a/strbuf.h b/strbuf.h
index 14c8c10d66..cd7ad898eb 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -70,6 +70,12 @@ struct strbuf {
 extern char strbuf_slopbuf[];
 #define STRBUF_INIT  { .alloc = 0, .len = 0, .buf = strbuf_slopbuf }
 
+/*
+ * Predeclare this here, since cache.h includes this file before it defines the
+ * struct.
+ */
+struct object_id;
+
 /**
  * Life Cycle Functions
  * --------------------
@@ -539,7 +545,7 @@ extern void strbuf_list_free(struct strbuf **);
  * the strbuf `sb`.
  */
 extern void strbuf_add_unique_abbrev(struct strbuf *sb,
-				     const unsigned char *sha1,
+				     const struct object_id *oid,
 				     int abbrev_len);
 
 /**
diff --git a/submodule.c b/submodule.c
index 12a2503fda..c210640d35 100644
--- a/submodule.c
+++ b/submodule.c
@@ -540,9 +540,9 @@ static void show_submodule_header(struct diff_options *o, const char *path,
 
 output_header:
 	strbuf_addf(&sb, "Submodule %s ", path);
-	strbuf_add_unique_abbrev(&sb, one->hash, DEFAULT_ABBREV);
+	strbuf_add_unique_abbrev(&sb, one, DEFAULT_ABBREV);
 	strbuf_addstr(&sb, (fast_backward || fast_forward) ? ".." : "...");
-	strbuf_add_unique_abbrev(&sb, two->hash, DEFAULT_ABBREV);
+	strbuf_add_unique_abbrev(&sb, two, DEFAULT_ABBREV);
 	if (message)
 		strbuf_addf(&sb, " %s\n", message);
 	else
diff --git a/transport.c b/transport.c
index 00d48b5b56..87de35dd5e 100644
--- a/transport.c
+++ b/transport.c
@@ -367,7 +367,7 @@ static void print_ok_ref_status(struct ref *ref, int porcelain, int summary_widt
 		char type;
 		const char *msg;
 
-		strbuf_add_unique_abbrev(&quickref, ref->old_oid.hash,
+		strbuf_add_unique_abbrev(&quickref, &ref->old_oid,
 					 DEFAULT_ABBREV);
 		if (ref->forced_update) {
 			strbuf_addstr(&quickref, "...");
@@ -378,7 +378,7 @@ static void print_ok_ref_status(struct ref *ref, int porcelain, int summary_widt
 			type = ' ';
 			msg = NULL;
 		}
-		strbuf_add_unique_abbrev(&quickref, ref->new_oid.hash,
+		strbuf_add_unique_abbrev(&quickref, &ref->new_oid,
 					 DEFAULT_ABBREV);
 
 		print_ref_status(type, quickref.buf, ref, ref->peer_ref, msg,
diff --git a/wt-status.c b/wt-status.c
index 66f4234af1..5c685b6165 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1188,7 +1188,7 @@ static void abbrev_sha1_in_line(struct strbuf *line)
 		strbuf_trim(split[1]);
 		if (!get_oid(split[1]->buf, &oid)) {
 			strbuf_reset(split[1]);
-			strbuf_add_unique_abbrev(split[1], oid.hash,
+			strbuf_add_unique_abbrev(split[1], &oid,
 						 DEFAULT_ABBREV);
 			strbuf_addch(split[1], ' ');
 			strbuf_reset(line);
@@ -1422,7 +1422,7 @@ static char *get_branch(const struct worktree *wt, const char *path)
 		;
 	else if (!get_oid_hex(sb.buf, &oid)) {
 		strbuf_reset(&sb);
-		strbuf_add_unique_abbrev(&sb, oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&sb, &oid, DEFAULT_ABBREV);
 	} else if (!strcmp(sb.buf, "detached HEAD")) /* rebase */
 		goto got_nothing;
 	else			/* bisect */
@@ -1459,7 +1459,7 @@ static int grab_1st_switch(struct object_id *ooid, struct object_id *noid,
 	if (!strcmp(cb->buf.buf, "HEAD")) {
 		/* HEAD is relative. Resolve it to the right reflog entry. */
 		strbuf_reset(&cb->buf);
-		strbuf_add_unique_abbrev(&cb->buf, noid->hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&cb->buf, noid, DEFAULT_ABBREV);
 	}
 	return 1;
 }