diff --git a/src/common/runtime.cpp b/src/common/runtime.cpp
index 8ee32ee39..e7ba8bd9a 100644
--- a/src/common/runtime.cpp
+++ b/src/common/runtime.cpp
@@ -645,7 +645,7 @@ extern "C" int luax_typerror(lua_State *L, int narg, const char *tname)
 	return luaL_argerror(L, narg, msg);
 }
 
-int luax_objlen(lua_State *L, int ndx)
+size_t luax_objlen(lua_State *L, int ndx)
 {
 #if LUA_VERSION_NUM == 501
 	return lua_objlen(L, ndx);
diff --git a/src/common/runtime.h b/src/common/runtime.h
index 9868ff6d7..f0facdeee 100644
--- a/src/common/runtime.h
+++ b/src/common/runtime.h
@@ -397,7 +397,7 @@ extern "C" { // Also called from luasocket
 /**
  * Calls luax_objlen/lua_rawlen depending on version
  **/
-int luax_objlen(lua_State *L, int ndx);
+size_t luax_objlen(lua_State *L, int ndx);
 
 extern "C" { // Called by enet and luasocket
 	void luax_register(lua_State *L, const char *name, const luaL_Reg *l);