diff --git a/language/interfaces/idefinesandincludesmanager.h b/language/interfaces/idefinesandincludesmanager.h
index e39b4b1f1d..154efa9a4f 100644
--- a/language/interfaces/idefinesandincludesmanager.h
+++ b/language/interfaces/idefinesandincludesmanager.h
@@ -1,70 +1,106 @@
 /*
  * This file is part of KDevelop
  *
  * Copyright 2014 Sergey Kalinichev <kalinichev.so.0@gmail.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
  * of the License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  * 02110-1301, USA.
  */
 
 #ifndef IDEFINESANDINCLUDES_H
 #define IDEFINESANDINCLUDES_H
 
 #include <QHash>
 #include <QString>
 #include <QStringList>
 
 #include <KConfigGroup>
 
 #include <util/path.h>
 
 #include "../languageexport.h"
 
 namespace KDevelop
 {
 class ProjectBaseItem;
+class IProject;
 
 typedef QHash<QString, QVariant> Defines;
 struct ConfigEntry
 {
     QString path;
     QStringList includes;
     Defines defines;
 
     ConfigEntry( const QString& path = QString() ) : path( path ) {}
 };
 
-/** An interface that provides language plugins with user specified include directories/files and defines.
+/** An interface that provides language plugins with include directories/files and defines.
 * Call IDefinesAndIncludesManager::manager() to get the instance of the plugin.
+* NOTE: None of the methods in this interface is thread-safe.
 **/
 class KDEVPLATFORMLANGUAGE_EXPORT IDefinesAndIncludesManager
 {
 public:
-    ///@return list of all custom defines for @p item
-    virtual QHash<QString, QString> defines( const ProjectBaseItem* item ) const = 0;
+    /// The type of includes/defines
+    enum Type {
+        CompilerSpecific = 1, ///< Those that compiler provides
+        ProjectSpecific = 2, ///< Those that project manager provides
+        UserDefined = 4,    ///< Those that user defines
+        All = CompilerSpecific | ProjectSpecific | UserDefined
+     };
 
-    ///@return list of all custom includes for @p item
-    virtual Path::List includes( const ProjectBaseItem* item ) const = 0;
+    /// Class that actually does all the work of calculating i/d.
+    /// Implement one in e.g. project manager and register it with @see registerProvider
+    /// To unregister it use @see unregisterProvider
+    class Provider
+    {
+    public:
+        virtual ~Provider() = default;
 
-    ///@return instance of the plugin if one is loaded, nullptr otherwise
+        virtual QHash<QString, QString> defines( ProjectBaseItem* item ) const = 0;
+
+        virtual Path::List includes( ProjectBaseItem* item ) const = 0;
+
+        /// @return the type of i/d this provider provides
+        virtual Type type() const = 0;
+    };
+
+    ///@return list of defines for @p item
+    virtual QHash<QString, QString> defines( ProjectBaseItem* item, Type type = All ) const = 0;
+
+    ///@return list of include directories/files for @p item
+    virtual Path::List includes( ProjectBaseItem* item, Type type = All ) const = 0;
+
+    ///@return the instance of the plugin.
     static IDefinesAndIncludesManager* manager();
 
     virtual ~IDefinesAndIncludesManager();
+
+    /// Register the @p provider
+    virtual void registerProvider(Provider* provider) = 0;
+
+     /**
+     * Unregister the provider
+     *
+     * @return true on success, false otherwise (e.g. if not registered)
+     */
+    virtual bool unregisterProvider(Provider* provider) = 0;
 };
 }
 
 Q_DECLARE_INTERFACE( KDevelop::IDefinesAndIncludesManager, "org.kdevelop.IDefinesAndIncludesManager" )
 
 #endif