diff --git a/src/main/java/com/annimon/ownlang/lib/ClassDeclarations.java b/src/main/java/com/annimon/ownlang/lib/ClassDeclarations.java
index 1335b1b..b079ef3 100644
--- a/src/main/java/com/annimon/ownlang/lib/ClassDeclarations.java
+++ b/src/main/java/com/annimon/ownlang/lib/ClassDeclarations.java
@@ -1,15 +1,14 @@
 package com.annimon.ownlang.lib;
 
-import com.annimon.ownlang.exceptions.UnknownFunctionException;
 import com.annimon.ownlang.parser.ast.ClassDeclarationStatement;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public final class ClassDeclarations {
 
     private static final Map<String, ClassDeclarationStatement> declarations;
     static {
-        declarations = new HashMap<>();
+        declarations = new ConcurrentHashMap<>();
     }
 
     private ClassDeclarations() { }
@@ -22,12 +21,7 @@ public final class ClassDeclarations {
         return declarations;
     }
     
-    public static boolean isExists(String key) {
-        return declarations.containsKey(key);
-    }
-    
     public static ClassDeclarationStatement get(String key) {
-        if (!isExists(key)) throw new UnknownFunctionException(key);
         return declarations.get(key);
     }
     
diff --git a/src/main/java/com/annimon/ownlang/lib/Instantiable.java b/src/main/java/com/annimon/ownlang/lib/Instantiable.java
new file mode 100644
index 0000000..709b4c7
--- /dev/null
+++ b/src/main/java/com/annimon/ownlang/lib/Instantiable.java
@@ -0,0 +1,9 @@
+package com.annimon.ownlang.lib;
+
+/**
+ * Interface for values that supports creating instances with `new` keyword.
+ */
+public interface Instantiable {
+    
+    Value newInstance(Value[] args);
+}
diff --git a/src/main/java/com/annimon/ownlang/modules/java/java.java b/src/main/java/com/annimon/ownlang/modules/java/java.java
index c8f7822..58ef5fc 100644
--- a/src/main/java/com/annimon/ownlang/modules/java/java.java
+++ b/src/main/java/com/annimon/ownlang/modules/java/java.java
@@ -103,7 +103,7 @@ public final class java implements Module {
         }
     }
 
-    private static class ClassValue extends MapValue {
+    private static class ClassValue extends MapValue implements Instantiable {
 
         public static Value classOrNull(Class<?> clazz) {
             if (clazz == null) return NULL;
@@ -162,7 +162,8 @@ public final class java implements Module {
             return NumberValue.fromBoolean(clazz.isAssignableFrom( ((ClassValue)args[0]).clazz ));
         }
 
-        private Value newInstance(Value[] args) {
+        @Override
+        public Value newInstance(Value[] args) {
             return findConstructorAndInstantiate(args, clazz.getConstructors());
         }
 
diff --git a/src/main/java/com/annimon/ownlang/parser/ast/ObjectCreationExpression.java b/src/main/java/com/annimon/ownlang/parser/ast/ObjectCreationExpression.java
index e5edc27..6e15ad0 100644
--- a/src/main/java/com/annimon/ownlang/parser/ast/ObjectCreationExpression.java
+++ b/src/main/java/com/annimon/ownlang/parser/ast/ObjectCreationExpression.java
@@ -1,5 +1,6 @@
 package com.annimon.ownlang.parser.ast;
 
+import com.annimon.ownlang.exceptions.UnknownClassException;
 import com.annimon.ownlang.lib.*;
 import java.util.Iterator;
 import java.util.List;
@@ -17,6 +18,16 @@ public final class ObjectCreationExpression implements Expression {
     @Override
     public Value eval() {
         final ClassDeclarationStatement cd = ClassDeclarations.get(className);
+        if (cd == null) {
+            // Is Instantiable?
+            if (Variables.isExists(className)) {
+                final Value variable = Variables.get(className);
+                if (variable instanceof Instantiable) {
+                    return ((Instantiable) variable).newInstance(ctorArgs());
+                }
+            }
+            throw new UnknownClassException(className);
+        }
         
         // Create an instance and put evaluated fields with method declarations
         final ClassInstanceValue instance = new ClassInstanceValue(className);
@@ -30,14 +41,17 @@ public final class ObjectCreationExpression implements Expression {
         }
         
         // Call a constructor
+        instance.callConstructor(ctorArgs());
+        return instance;
+    }
+    
+    private Value[] ctorArgs() {
         final int argsSize = constructorArguments.size();
         final Value[] ctorArgs = new Value[argsSize];
         for (int i = 0; i < argsSize; i++) {
             ctorArgs[i] = constructorArguments.get(i).eval();
         }
-        instance.callConstructor(ctorArgs);
-        
-        return instance;
+        return ctorArgs;
     }
     
     @Override