diff --git a/sources/reactphysics3d/mathematics/Quaternion.cpp b/sources/reactphysics3d/mathematics/Quaternion.cpp
index 54238f70..d87603fa 100755
--- a/sources/reactphysics3d/mathematics/Quaternion.cpp
+++ b/sources/reactphysics3d/mathematics/Quaternion.cpp
@@ -18,7 +18,8 @@
  ***************************************************************************/
 
 // Libraries
-#include "mathematics.h"
+#include "Quaternion.h"
+#include "Vector3D.h"
 #include <cassert>
 
 // Namespace
diff --git a/sources/reactphysics3d/mathematics/Vector3D.h b/sources/reactphysics3d/mathematics/Vector3D.h
index 9a7acc7c..c617ff89 100644
--- a/sources/reactphysics3d/mathematics/Vector3D.h
+++ b/sources/reactphysics3d/mathematics/Vector3D.h
@@ -22,6 +22,7 @@
 
 // Libraries
 #include <cmath>
+#include <cstdlib>
 #include "exceptions.h"
 #include "mathematics_functions.h"
 
@@ -130,7 +131,7 @@ inline Vector3D Vector3D::crossProduct(const Vector3D& vector) const {
 
 // Return true if two vectors are parallel
 inline bool Vector3D::isParallelWith(const Vector3D& vector) const {
-    return (approxEqual(this->scalarProduct(vector), length() * vector.length()));
+    return (approxEqual(abs(this->scalarProduct(vector)), length() * vector.length()));
 }
 
 // Overloaded operator for multiplication between a number and a Vector3D (inline)
diff --git a/sources/reactphysics3d/mathematics/mathematics.h b/sources/reactphysics3d/mathematics/mathematics.h
index 886c22af..118fd57b 100644
--- a/sources/reactphysics3d/mathematics/mathematics.h
+++ b/sources/reactphysics3d/mathematics/mathematics.h
@@ -25,14 +25,13 @@
 // Libraries
 #include "Matrix.h"
 #include "Matrix3x3.h"
-#include "Polygon3D.h"
 #include "Quaternion.h"
-#include "Segment3D.h"
 #include "Vector.h"
 #include "Vector3D.h"
 #include "constants.h"
 #include "exceptions.h"
 #include "mathematics_functions.h"
+#include <vector>
 #include <cstdio>
 #include <cassert>
 #include <cmath>
@@ -172,6 +171,7 @@ inline std::vector<reactphysics3d::Vector3D> movePoints(const std::vector<reactp
     return result;
 }
 
+
 // TODO : Test this method
 // Compute the projection of a set of 3D points onto a 3D plane. The set of points is given by "points" and the plane is given by
 // a point "A" and a normal vector "normal". This method returns the initial set of points projected onto the plane.
@@ -311,7 +311,6 @@ inline std::vector<reactphysics3d::Vector3D> clipSegmentWithRectangleInPlane(con
     return outputSegment;
 }
 
-
 // TODO : Test this method
 // This method uses the Sutherland-Hodgman clipping algorithm to clip a subject polygon (given by the ordered 3D vertices in "subjectPolygon") using
 // a rectangle polygon (given by the ordered 3D vertices in "clipRectangle"). The subject polygon and the clip rectangle are in 3D but we assumed that
@@ -367,5 +366,6 @@ inline std::vector<reactphysics3d::Vector3D> clipPolygonWithRectangleInPlane(con
 }
 
 } // End of the ReactPhysics3D namespace
+
 
 #endif