diff --git a/criu/cr-service.c b/criu/cr-service.c
index e6aac232e7..717fd95faa 100644
--- a/criu/cr-service.c
+++ b/criu/cr-service.c
@@ -674,7 +674,7 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
 	}
 
 	/*
-	 * open images_dir - images_dir_fd is a required RPC parameter
+	 * open images_dir - images_dir_fd is -1 by default
 	 *
 	 * This assumes that if opts.imgs_dir is set we have a value
 	 * from the configuration file parser. The test to see that
diff --git a/images/rpc.proto b/images/rpc.proto
index 1a4722a9ce..fac5f6e647 100644
--- a/images/rpc.proto
+++ b/images/rpc.proto
@@ -61,7 +61,7 @@ enum criu_pre_dump_mode {
 };
 
 message criu_opts {
-	required int32			images_dir_fd	= 1 [default = -1];
+	optional int32			images_dir_fd	= 1 [default = -1];
 	optional string			images_dir	= 68; /* used only if images_dir_fd == -1 */
 	optional int32			pid		= 2; /* if not set on dump, will dump requesting process */