diff --git a/modules/img/base/src/image_state/image_state_impl.hh b/modules/img/base/src/image_state/image_state_impl.hh
index d18989aaa3f6722617b01893fc765a6603bdfa25..e3a70ae93ca6b402b4d708189b97742d51855207 100644
--- a/modules/img/base/src/image_state/image_state_impl.hh
+++ b/modules/img/base/src/image_state/image_state_impl.hh
@@ -81,7 +81,7 @@ public:
   // image state base interface
   virtual ImageStateBasePtr Clone(bool cc=true) const;
   
-  virtual size_t MemSize() const;
+  virtual std::size_t MemSize() const;
 
   virtual DataType GetType() const;
 
@@ -168,10 +168,10 @@ public:
   const T& Value(const Index& i) const;
 
   // pass-through to value holder
-  T& Value(size_t i);
+  T& Value(std::size_t i);
 
   // pass-through to value holder
-  const T& Value(size_t i) const;
+  const T& Value(std::size_t i) const;
 
   //! direct access to value holder
   ValueHolder<T>& Data();
diff --git a/modules/img/base/src/image_state/value_holder.cc b/modules/img/base/src/image_state/value_holder.cc
index aafae4b5412428571a0e0f24bcfde72443cd58fd..b17acccbc93758dfaca5b0fda583e2f8569b0953 100644
--- a/modules/img/base/src/image_state/value_holder.cc
+++ b/modules/img/base/src/image_state/value_holder.cc
@@ -42,7 +42,7 @@ namespace ost { namespace img { namespace image_state {
 namespace {
 
 template <typename V>
-size_t calc_volume(const Size& s)
+std::size_t calc_volume(const Size& s)
 {
   unsigned int tmp;
   unsigned int numbits = 0;
@@ -67,11 +67,11 @@ size_t calc_volume(const Size& s)
   {
     ++numbits;
   }
-  // check if number of pixels (2**(numbits+1)) larger than what size_t can handle
-  if(numbits>=sizeof(size_t)*8){
+  // check if number of pixels (2**(numbits+1)) larger than what std::size_t can handle
+  if(numbits>=sizeof(std::size_t)*8){
       throw std::bad_alloc();
   }
-  return static_cast<size_t>(s[0])*static_cast<size_t>(s[1])*static_cast<size_t>(s[2]);
+  return static_cast<std::size_t>(s[0])*static_cast<std::size_t>(s[1])*static_cast<std::size_t>(s[2]);
 }
 
 } //ns
@@ -183,7 +183,7 @@ DataType ValueHolder<V>::GetDataType()
 }
 
 template <typename V>
-size_t ValueHolder<V>::MemSize() const
+std::size_t ValueHolder<V>::MemSize() const
 {
   return sizeof(V)*data_.size();
 }
diff --git a/modules/img/base/src/image_state/value_holder.hh b/modules/img/base/src/image_state/value_holder.hh
index 6caa155cc9fe254dd962d198685347aa60de1e22..cb154c2e16f968b40141aa511d00e9a9b9bdf226 100644
--- a/modules/img/base/src/image_state/value_holder.hh
+++ b/modules/img/base/src/image_state/value_holder.hh
@@ -95,7 +95,7 @@ public:
 
   static DataType GetDataType();
 
-  size_t  MemSize() const;
+  std::size_t  MemSize() const;
 
 
 
@@ -124,11 +124,11 @@ public:
 
 private:
 #ifdef USE_ROW_ORDER
-  size_t depth_;
-  size_t height_depth_;
+  std::size_t depth_;
+  std::size_t height_depth_;
 #else
-  size_t height_;
-  size_t width_height_;
+  std::size_t height_;
+  std::size_t width_height_;
 #endif
 
   // actual data storage