diff --git a/Eigen/src/Geometry/Quaternion.h b/Eigen/src/Geometry/Quaternion.h
index faea62f17..73b28ae34 100644
--- a/Eigen/src/Geometry/Quaternion.h
+++ b/Eigen/src/Geometry/Quaternion.h
@@ -169,17 +169,32 @@ class QuaternionBase : public RotationBase<Derived, 3>
   /** return the result vector of \a v through the rotation*/
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Vector3 _transformVector(const Vector3& v) const;
 
+  #ifdef EIGEN_PARSED_BY_DOXYGEN
   /** \returns \c *this with scalar type casted to \a NewScalarType
     *
     * Note that if \a NewScalarType is equal to the current scalar type of \c *this
     * then this function smartly returns a const reference to \c *this.
     */
   template<typename NewScalarType>
-  EIGEN_DEVICE_FUNC inline typename internal::cast_return_type<Derived,Quaternion<NewScalarType> >::type cast() const
+  EIGEN_DEVICE_FUNC inline typename internal::cast_return_type<Derived,Quaternion<NewScalarType> >::type cast() const;
+
+  #else
+
+  template<typename NewScalarType>
+  EIGEN_DEVICE_FUNC inline 
+  typename internal::enable_if<internal::is_same<Scalar,NewScalarType>::value,const Derived&>::type cast() const
   {
-    return typename internal::cast_return_type<Derived,Quaternion<NewScalarType> >::type(derived());
+    return derived();
   }
 
+  template<typename NewScalarType>
+  EIGEN_DEVICE_FUNC inline 
+  typename internal::enable_if<!internal::is_same<Scalar,NewScalarType>::value,Quaternion<NewScalarType> >::type cast() const
+  {
+    return Quaternion<NewScalarType>(coeffs().template cast<NewScalarType>());
+  }
+  #endif
+
 #ifdef EIGEN_QUATERNIONBASE_PLUGIN
 # include EIGEN_QUATERNIONBASE_PLUGIN
 #endif
diff --git a/test/geo_quaternion.cpp b/test/geo_quaternion.cpp
index 27219db10..1da683c0e 100644
--- a/test/geo_quaternion.cpp
+++ b/test/geo_quaternion.cpp
@@ -245,6 +245,14 @@ template<typename Scalar> void mapQuaternion(void){
   // is used to determine whether we can return a coeff by reference or not, which is not enough for Map<const ...>.
   //const MCQuaternionUA& cmcq3(mcq3);
   //VERIFY( &cmcq3.x() == &mcq3.x() );
+
+  // test cast
+  {
+    Quaternion<float> q1f = mq1.template cast<float>();
+    VERIFY_IS_APPROX(q1f.template cast<Scalar>(),mq1);
+    Quaternion<double> q1d = mq1.template cast<double>();
+    VERIFY_IS_APPROX(q1d.template cast<Scalar>(),mq1);
+  }
 }
 
 template<typename Scalar> void quaternionAlignment(void){