diff --git a/coding/reader.cpp b/coding/reader.cpp
index 81cbdcced5..6b94af3bc7 100644
--- a/coding/reader.cpp
+++ b/coding/reader.cpp
@@ -19,19 +19,3 @@ bool Reader::IsEqual(string const & name1, string const & name2)
   return (name1 == name2);
 #endif
 }
-
-namespace
-{
-  bool AssertPosAndSizeImpl(uint64_t pos, uint64_t size, uint64_t readerSize)
-  {
-    bool const ret1 = (pos + size <= readerSize);
-    bool const ret2 = (size <= static_cast<size_t>(-1));
-    ASSERT ( ret1 && ret2, (pos, size, readerSize) );
-    return (ret1 && ret2);
-  }
-}
-
-bool MemReader::AssertPosAndSize(uint64_t pos, uint64_t size) const
-{
-  return AssertPosAndSizeImpl(pos, size, Size());
-}
diff --git a/coding/reader.hpp b/coding/reader.hpp
index c96088d0ff..34d2d98ac0 100644
--- a/coding/reader.hpp
+++ b/coding/reader.hpp
@@ -32,13 +32,12 @@ public:
 };
 
 // Reader from memory.
-class MemReader : public Reader
+template <bool WithExceptions>
+class MemReaderTemplate : public Reader
 {
-  bool AssertPosAndSize(uint64_t pos, uint64_t size) const;
-
 public:
   // Construct from block of memory.
-  MemReader(void const * pData, size_t size)
+  MemReaderTemplate(void const * pData, size_t size)
     : m_pData(static_cast<char const *>(pData)), m_size(size)
   {
   }
@@ -50,27 +49,51 @@ public:
 
   inline void Read(uint64_t pos, void * p, size_t size) const override
   {
-    ASSERT ( AssertPosAndSize(pos, size), () );
+    AssertPosAndSize(pos, size);
     memcpy(p, m_pData + pos, size);
   }
 
-  inline MemReader SubReader(uint64_t pos, uint64_t size) const
+  inline MemReaderTemplate SubReader(uint64_t pos, uint64_t size) const
   {
-    ASSERT ( AssertPosAndSize(pos, size), () );
-    return MemReader(m_pData + pos, static_cast<size_t>(size));
+    AssertPosAndSize(pos, size);
+    return MemReaderTemplate(m_pData + pos, static_cast<size_t>(size));
   }
 
   inline unique_ptr<Reader> CreateSubReader(uint64_t pos, uint64_t size) const override
   {
-    ASSERT ( AssertPosAndSize(pos, size), () );
-    return make_unique<MemReader>(m_pData + pos, static_cast<size_t>(size));
+    AssertPosAndSize(pos, size);
+    return make_unique<MemReaderTemplate>(m_pData + pos, static_cast<size_t>(size));
   }
 
 private:
+  bool GoodPosAndSize(uint64_t pos, uint64_t size) const
+  {
+    uint64_t const readerSize = Size();
+    bool const ret1 = (pos + size <= readerSize);
+    bool const ret2 = (size <= static_cast<size_t>(-1));
+    return ret1 && ret2;
+  }
+
+  void AssertPosAndSize(uint64_t pos, uint64_t size) const
+  {
+    if (WithExceptions)
+    {
+      if (!GoodPosAndSize(pos, size))
+        MYTHROW(Reader::SizeException, (pos, size, Size()));
+    }
+    else
+    {
+      ASSERT(GoodPosAndSize(pos, size), (pos, size, Size()));
+    }
+  }
+
   char const * m_pData;
   size_t m_size;
 };
 
+using MemReader = MemReaderTemplate<false>;
+using MemReaderWithExceptions = MemReaderTemplate<true>;
+
 // Reader wrapper to hold the pointer to a polymorfic reader.
 // Common use: ReaderSource<ReaderPtr<Reader> >.
 // Note! It takes the ownership of Reader.