diff --git a/src/Base/CoordinateSystem.cpp b/src/Base/CoordinateSystem.cpp
index cfd7ee9e69..7914335d99 100644
--- a/src/Base/CoordinateSystem.cpp
+++ b/src/Base/CoordinateSystem.cpp
@@ -25,6 +25,7 @@
 
 #include "CoordinateSystem.h"
 #include "Exception.h"
+#include "Matrix.h"
 
 
 using namespace Base;
diff --git a/src/Base/Placement.cpp b/src/Base/Placement.cpp
index 9128ecc381..43867887cc 100644
--- a/src/Base/Placement.cpp
+++ b/src/Base/Placement.cpp
@@ -23,6 +23,7 @@
 #include "PreCompiled.h"
 
 #include "Placement.h"
+#include "Matrix.h"
 #include "Rotation.h"
 #include "DualQuaternion.h"
 
diff --git a/src/Base/Placement.h b/src/Base/Placement.h
index 4bd5670338..2020096214 100644
--- a/src/Base/Placement.h
+++ b/src/Base/Placement.h
@@ -23,7 +23,6 @@
 #ifndef BASE_PLACEMENT_H
 #define BASE_PLACEMENT_H
 
-#include "Matrix.h"
 #include "Rotation.h"
 #include "Vector3D.h"
 
@@ -31,6 +30,7 @@
 namespace Base {
 
 class DualQuat;
+class Matrix4D;
 
 /**
  * The Placement class.
diff --git a/src/Base/Tools.h b/src/Base/Tools.h
index 79a21cf623..c5a6826941 100644
--- a/src/Base/Tools.h
+++ b/src/Base/Tools.h
@@ -35,7 +35,6 @@
 #include <string>
 #include <boost_signals2.hpp>
 #include <QString>
-#include <QObject>
 
 // ----------------------------------------------------------------------------