diff --git a/Eigen/Core b/Eigen/Core
index e532a00f8..e3c904e81 100644
--- a/Eigen/Core
+++ b/Eigen/Core
@@ -241,6 +241,8 @@ inline static const char *SimdInstructionSetsInUse(void) {
 // we use size_t frequently and we'll never remember to prepend it with std:: everytime just to
 // ensure QNX/QCC support
 using std::size_t;
+// gcc 4.6.0 wants std:: for ptrdiff_t 
+using std::ptrdiff_t;
 
 /** \defgroup Core_Module Core module
   * This is the main module of Eigen providing dense matrix and vector support
diff --git a/Eigen/src/Core/arch/AltiVec/Complex.h b/Eigen/src/Core/arch/AltiVec/Complex.h
index 5d16c9430..f8adf1b63 100644
--- a/Eigen/src/Core/arch/AltiVec/Complex.h
+++ b/Eigen/src/Core/arch/AltiVec/Complex.h
@@ -70,7 +70,7 @@ template<> EIGEN_STRONG_INLINE Packet2cf pset1<Packet2cf>(const std::complex<flo
 {
   Packet2cf res;
   /* On AltiVec we cannot load 64-bit registers, so wa have to take care of alignment */
-  if((std::ptrdiff_t(&from) % 16) == 0)
+  if((ptrdiff_t(&from) % 16) == 0)
     res.v = pload<Packet4f>((const float *)&from);
   else
     res.v = ploadu<Packet4f>((const float *)&from);
diff --git a/Eigen/src/Core/arch/AltiVec/PacketMath.h b/Eigen/src/Core/arch/AltiVec/PacketMath.h
index b814712f3..dc34ebbd6 100644
--- a/Eigen/src/Core/arch/AltiVec/PacketMath.h
+++ b/Eigen/src/Core/arch/AltiVec/PacketMath.h
@@ -296,14 +296,14 @@ template<> EIGEN_STRONG_INLINE Packet4i ploadu<Packet4i>(const int* from)
 template<> EIGEN_STRONG_INLINE Packet4f ploaddup<Packet4f>(const float*   from)
 {
   Packet4f p;
-  if((std::ptrdiff_t(&from) % 16) == 0)  p = pload<Packet4f>(from);
+  if((ptrdiff_t(&from) % 16) == 0)  p = pload<Packet4f>(from);
   else                              p = ploadu<Packet4f>(from);
   return vec_perm(p, p, p16uc_DUPLICATE);
 }
 template<> EIGEN_STRONG_INLINE Packet4i ploaddup<Packet4i>(const int*     from)
 {
   Packet4i p;
-  if((std::ptrdiff_t(&from) % 16) == 0)  p = pload<Packet4i>(from);
+  if((ptrdiff_t(&from) % 16) == 0)  p = pload<Packet4i>(from);
   else                              p = ploadu<Packet4i>(from);
   return vec_perm(p, p, p16uc_DUPLICATE);
 }
diff --git a/Eigen/src/StlSupport/details.h b/Eigen/src/StlSupport/details.h
index 2698361e8..397c8ef85 100644
--- a/Eigen/src/StlSupport/details.h
+++ b/Eigen/src/StlSupport/details.h
@@ -38,7 +38,7 @@ namespace Eigen {
   {
   public:
     typedef size_t    size_type;
-    typedef std::ptrdiff_t difference_type;
+    typedef ptrdiff_t difference_type;
     typedef T*        pointer;
     typedef const T*  const_pointer;
     typedef T&        reference;
diff --git a/test/mapstride.cpp b/test/mapstride.cpp
index 6c3097485..e2bda99ce 100644
--- a/test/mapstride.cpp
+++ b/test/mapstride.cpp
@@ -38,7 +38,7 @@ template<int Alignment,typename VectorType> void map_class_vector(const VectorTy
   Scalar* a_array = internal::aligned_new<Scalar>(arraysize+1);
   Scalar* array = a_array;
   if(Alignment!=Aligned)
-    array = (Scalar*)(std::ptrdiff_t(a_array) + (internal::packet_traits<Scalar>::AlignedOnScalar?sizeof(Scalar):sizeof(typename NumTraits<Scalar>::Real)));
+    array = (Scalar*)(ptrdiff_t(a_array) + (internal::packet_traits<Scalar>::AlignedOnScalar?sizeof(Scalar):sizeof(typename NumTraits<Scalar>::Real)));
 
   {
     Map<VectorType, Alignment, InnerStride<3> > map(array, size);
@@ -77,7 +77,7 @@ template<int Alignment,typename MatrixType> void map_class_matrix(const MatrixTy
   Scalar* a_array = internal::aligned_new<Scalar>(arraysize+1);
   Scalar* array = a_array;
   if(Alignment!=Aligned)
-    array = (Scalar*)(std::ptrdiff_t(a_array) + (internal::packet_traits<Scalar>::AlignedOnScalar?sizeof(Scalar):sizeof(typename NumTraits<Scalar>::Real)));
+    array = (Scalar*)(ptrdiff_t(a_array) + (internal::packet_traits<Scalar>::AlignedOnScalar?sizeof(Scalar):sizeof(typename NumTraits<Scalar>::Real)));
 
   // test no inner stride and some dynamic outer stride
   {
diff --git a/unsupported/Eigen/FFT b/unsupported/Eigen/FFT
index c8f14d845..0b2823058 100644
--- a/unsupported/Eigen/FFT
+++ b/unsupported/Eigen/FFT
@@ -393,7 +393,7 @@ class FFT
       for (int k=0;k<nx;++k)
         *x++ *= s;
 #else
-      if ( ((std::ptrdiff_t)x) & 15 )
+      if ( ((ptrdiff_t)x) & 15 )
         Matrix<T_Data, Dynamic, 1>::Map(x,nx) *= s;
       else
         Matrix<T_Data, Dynamic, 1>::MapAligned(x,nx) *= s;