diff --git a/Documentation/gitprotocol-v2.adoc b/Documentation/gitprotocol-v2.adoc
index befa697d21..f21a6cbcaa 100644
--- a/Documentation/gitprotocol-v2.adoc
+++ b/Documentation/gitprotocol-v2.adoc
@@ -568,21 +568,26 @@ An `object-info` request takes the following arguments:
 
 	oid <oid>
 	Indicates to the server an object which the client wants to obtain
-	information for.
+	information for. They must be full object IDs.
 
 The response of `object-info` is a list of the requested object ids
 and associated requested information, each separated by a single space.
 
 	output = info flush-pkt
 
-	info = PKT-LINE(attrs) LF)
+	info = PKT-LINE(attrs LF)
 		*PKT-LINE(obj-info LF)
 
 	attrs = attr | attrs SP attrs
 
+	obj-size = 1*DIGIT
+
 	attr = "size"
 
-	obj-info = obj-id SP obj-size
+	obj-info = obj-id SP [obj-size]
+
+	If the server does not recognize the object id, the response will be
+	`obj-id SP` regardless of the number of attributes requested.
 
 bundle-uri
 ~~~~~~~~~~
diff --git a/serve.c b/serve.c
index 49a6e39b1d..2b07d922b3 100644
--- a/serve.c
+++ b/serve.c
@@ -89,7 +89,7 @@ static void session_id_receive(struct repository *r UNUSED,
 	trace2_data_string("transfer", NULL, "client-sid", client_sid);
 }
 
-static int object_info_advertise(struct repository *r, struct strbuf *value UNUSED)
+static int object_info_advertise(struct repository *r, struct strbuf *value)
 {
 	if (advertise_object_info == -1 &&
 	    repo_config_get_bool(r, "transfer.advertiseobjectinfo",
@@ -97,6 +97,9 @@ static int object_info_advertise(struct repository *r, struct strbuf *value UNUS
 		/* disabled by default */
 		advertise_object_info = 0;
 	}
+	/* Currently only size is supported */
+	if (value && advertise_object_info)
+		strbuf_addstr(value, "size");
 	return advertise_object_info;
 }