diff --git a/src/main/java/chocopy/pa2/TypeChecker.java b/src/main/java/chocopy/pa2/TypeChecker.java
index c131a60..5e93485 100644
--- a/src/main/java/chocopy/pa2/TypeChecker.java
+++ b/src/main/java/chocopy/pa2/TypeChecker.java
@@ -98,17 +98,21 @@ public class TypeChecker extends AbstractNodeAnalyzer<Type> {
             {
                 err(node, "Expression `%s` type inference error.", ex);
                 error = true;
-            } else if (ex instanceof IndexExpr && 
-                ((IndexExpr)ex).list.getInferredType().equals(Type.STR_TYPE)){
+            } 
+            else if (ex instanceof IndexExpr && 
+                ((IndexExpr)ex).list.getInferredType().equals(Type.STR_TYPE))
+            {
                 err(ex, "`str` is not a list type");
                 error = true;
             }
-            else if(tr!=null && tl.isListType() && tr.isListType()){
+            else if(tr!=null && tl.isListType() && tr.isListType())
+            {
                 if(!((!tl.elementType().isSpecialType()&&tr.elementType().equals(Type.NONE_TYPE))||
-                    tl.equals(tr)||tr.elementType().equals(Type.EMPTY_TYPE))){
-                    err(node, "Expected type `%s`; got type `%s`", tl, tr);
+                    tl.equals(tr)||tr.elementType().equals(Type.EMPTY_TYPE)))
+                    {
+                        err(node, "Expected type `%s`; got type `%s`", tl, tr);
                     error = true;
-                }
+                    }
             }
             else if(tl.isListType() && Type.EMPTY_TYPE.equals(tr)) ; //continue;
             else if(tr != null && !(StudentAnalysis.subClassOf(tl, tr, currentScope) || !tl.isSpecialType() && tr.equals(Type.NONE_TYPE)))
@@ -302,7 +306,7 @@ public class TypeChecker extends AbstractNodeAnalyzer<Type> {
                 Type thisArgTy = thisArg.setInferredType(thisArg.dispatch(this)), 
                      thisParamTy = funcTy.parameters.get(i + 1);
 
-                if(!thisParamTy.equals(thisArgTy))
+                if(!thisParamTy.equals(thisArgTy) && !StudentAnalysis.subClassOf(thisParamTy, thisArgTy, currentScope))
                     err(node, "Expected type `%s`; got type `%s` in parameter %d", 
                             thisParamTy, thisArgTy, i + 1);
             }