diff --git a/lib/base/array.cpp b/lib/base/array.cpp
index c6a79bf4a..6b4ad2114 100644
--- a/lib/base/array.cpp
+++ b/lib/base/array.cpp
@@ -115,7 +115,7 @@ size_t Array::GetLength(void) const
  * @param value The value.
  * @returns true if the array contains the value, false otherwise.
  */
-bool Array::Contains(const String& value) const
+bool Array::Contains(const Value& value) const
 {
 	ASSERT(!OwnsLock());
 	ObjectLock olock(this);
diff --git a/lib/base/array.hpp b/lib/base/array.hpp
index 7459348ab..e721cc0e6 100644
--- a/lib/base/array.hpp
+++ b/lib/base/array.hpp
@@ -53,7 +53,7 @@ public:
 	Iterator End(void);
 
 	size_t GetLength(void) const;
-	bool Contains(const String& value) const;
+	bool Contains(const Value& value) const;
 
 	void Insert(unsigned int index, const Value& value);
 	void Remove(unsigned int index);
diff --git a/lib/config/expression.cpp b/lib/config/expression.cpp
index 7135e4c64..d3f6914e3 100644
--- a/lib/config/expression.cpp
+++ b/lib/config/expression.cpp
@@ -200,14 +200,7 @@ Value InExpression::DoEvaluate(const Object::Ptr& context, DebugHint *dhint) con
 	Value left = m_Operand1->Evaluate(context);
 		
 	Array::Ptr arr = right;
-	ObjectLock olock(arr);
-	BOOST_FOREACH(const Value& value, arr) {
-		if (value == left) {
-			return true;
-		}
-	}
-
-	return false;
+	return arr->Contains(left);
 }
 
 Value NotInExpression::DoEvaluate(const Object::Ptr& context, DebugHint *dhint) const
@@ -222,13 +215,7 @@ Value NotInExpression::DoEvaluate(const Object::Ptr& context, DebugHint *dhint)
 	Value left = m_Operand1->Evaluate(context);
 
 	Array::Ptr arr = right;
-	ObjectLock olock(arr);
-	BOOST_FOREACH(const Value& value, arr) {
-		if (value == left)
-			return false;
-	}
-
-	return true;
+	return !arr->Contains(left);
 }
 
 Value LogicalAndExpression::DoEvaluate(const Object::Ptr& context, DebugHint *dhint) const