diff --git a/src/com/annimon/ownlang/lib/UserDefinedFunction.java b/src/com/annimon/ownlang/lib/UserDefinedFunction.java
index d8686ee..fabe27b 100644
--- a/src/com/annimon/ownlang/lib/UserDefinedFunction.java
+++ b/src/com/annimon/ownlang/lib/UserDefinedFunction.java
@@ -28,12 +28,21 @@ public final class UserDefinedFunction implements Function {
     }
 
     @Override
-    public Value execute(Value... args) {
+    public Value execute(Value... values) {
+        final int size = values.length;
+        if (size != getArgsCount()) throw new RuntimeException("Args count mismatch");
+
         try {
+            Variables.push();
+            for (int i = 0; i < size; i++) {
+                Variables.set(getArgsName(i), values[i]);
+            }
             body.execute();
             return NumberValue.ZERO;
         } catch (ReturnStatement rt) {
             return rt.getResult();
+        } finally {
+            Variables.pop();
         }
     }
 
diff --git a/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java b/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
index 554017a..f86681e 100644
--- a/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
+++ b/src/com/annimon/ownlang/parser/ast/FunctionalExpression.java
@@ -40,21 +40,7 @@ public final class FunctionalExpression implements Expression {
         for (int i = 0; i < size; i++) {
             values[i] = arguments.get(i).eval();
         }
-        
-        final Function function = getFunction(name);
-        if (function instanceof UserDefinedFunction) {
-            final UserDefinedFunction userFunction = (UserDefinedFunction) function;
-            if (size != userFunction.getArgsCount()) throw new RuntimeException("Args count mismatch");
-            
-            Variables.push();
-            for (int i = 0; i < size; i++) {
-                Variables.set(userFunction.getArgsName(i), values[i]);
-            }
-            final Value result = userFunction.execute(values);
-            Variables.pop();
-            return result;
-        }
-        return function.execute(values);
+        return getFunction(name).execute(values);
     }
     
     private Function getFunction(String key) {