diff --git a/MindState.lua b/MindState.lua
index fa05b1c..1738403 100644
--- a/MindState.lua
+++ b/MindState.lua
@@ -42,11 +42,14 @@ end
 function StatefulObject:gotoState(stateName)
   assert(self.states~=nil, "Attribute 'states' not detected. check that you called instance:gotoState and not instance.gotoState, and that you invoked super(self) in the constructor.")
 
-  local nextState = self.states[stateName]
-  assert(type(stateName)=='string' and nextState~=nil, "State '" .. stateName .. "' not found")
+  local nextState
+  if(stateName~=nil) then
+    nextState = self.states[stateName]
+    assert(nextState~=nil, "State '" .. stateName .. "' not found")
+  end
 
   local prevState = self.currentState
-  if(prevState~=nil and type(prevState.exitState) == "function") then
+  if(prevState~=nil and type(prevState.exitState) == "function") then
     prevState.exitState(self)
   end