diff --git a/lualib-src/lua-bson.c b/lualib-src/lua-bson.c
index 88f1be8e..37b5f7f6 100644
--- a/lualib-src/lua-bson.c
+++ b/lualib-src/lua-bson.c
@@ -1135,15 +1135,18 @@ lobjectid(lua_State *L) {
 		}
 	} else {
 		time_t ti = time(NULL);
+		uint32_t id = oid_counter;
+		// old_counter is a static var, use atom inc.
+		__sync_add_and_fetch(&oid_counter,1);
+
 		oid[2] = (ti>>24) & 0xff;
 		oid[3] = (ti>>16) & 0xff;
 		oid[4] = (ti>>8) & 0xff;
 		oid[5] = ti & 0xff;
 		memcpy(oid+6 , oid_header, 5);
-		oid[11] = (oid_counter>>16) & 0xff; 
-		oid[12] = (oid_counter>>8) & 0xff; 
-		oid[13] = oid_counter & 0xff; 
-		++oid_counter;
+		oid[11] = (id>>16) & 0xff; 
+		oid[12] = (id>>8) & 0xff; 
+		oid[13] = id & 0xff;
 	}
 	lua_pushlstring( L, (const char *)oid, 14);