diff --git a/include/itkInputStreamBase.h b/include/itkInputStreamBase.h
index f06fc0a44..04ae73268 100644
--- a/include/itkInputStreamBase.h
+++ b/include/itkInputStreamBase.h
@@ -18,12 +18,10 @@
 #ifndef itkInputStreamBase_h
 #define itkInputStreamBase_h
 
-#include "itkPipeline.h"
-#include "itkWasmStringStream.h"
-
+#include <ios>
+#include <iosfwd> // For istream.
+#include <memory> // For unique_ptr.
 #include <string>
-#include <sstream>
-#include <fstream>
 
 #include "WebAssemblyInterfaceExport.h"
 
@@ -54,52 +52,30 @@ class WebAssemblyInterface_EXPORT InputStreamBase
   std::istream *
   GetPointer()
   {
-    return m_IStream;
+    return m_IStream.get();
   }
 
   void
-  SetJSON(const std::string & json)
-  {
-    if (m_DeleteIStream && m_IStream != nullptr)
-    {
-      delete m_IStream;
-    }
-    m_DeleteIStream = false;
-    m_WasmStringStream = WasmStringStream::New();
-    m_WasmStringStream->SetJSON(json.c_str());
-
-    m_IStream = &(m_WasmStringStream->GetStringStream());
-  }
+  SetJSON(const std::string & json);
 
   virtual void
   SetFileName(const std::string & fileName) = 0;
 
 protected:
   void
-  SetFile(const std::string & fileName, const std::ios_base::openmode openMode)
-  {
-    if (m_DeleteIStream && m_IStream != nullptr)
-    {
-      delete m_IStream;
-    }
-    m_IStream = new std::ifstream(fileName, openMode);
-    m_DeleteIStream = true;
-  }
+  SetFile(const std::string & fileName, const std::ios_base::openmode openMode);
 
   InputStreamBase() = default;
-  virtual ~InputStreamBase()
-  {
-    if (m_DeleteIStream && m_IStream != nullptr)
-    {
-      delete m_IStream;
-    }
-  }
 
-private:
-  std::istream * m_IStream{ nullptr };
-  bool           m_DeleteIStream{ false };
+  // Move semantics for its derived classes:
+  InputStreamBase(InputStreamBase &&) = default;
+  InputStreamBase &
+  operator=(InputStreamBase &&) = default;
 
-  WasmStringStream::Pointer m_WasmStringStream;
+  virtual ~InputStreamBase();
+
+private:
+  std::unique_ptr<std::istream> m_IStream;
 };
 
 
diff --git a/src/itkInputStreamBase.cxx b/src/itkInputStreamBase.cxx
index 60050e230..8e3cd7cc7 100644
--- a/src/itkInputStreamBase.cxx
+++ b/src/itkInputStreamBase.cxx
@@ -16,16 +16,38 @@
  *
  *=========================================================================*/
 #include "itkInputStreamBase.h"
+#include "itkPipeline.h"
+#include "itkWasmStringStream.h"
 
-#include <string>
 #ifndef ITK_WASM_NO_MEMORY_IO
 #  include "itkWasmExports.h"
 #endif
 
+#include <fstream>
+#include <sstream>
+
 namespace itk
 {
 namespace wasm
 {
+void
+InputStreamBase::SetJSON(const std::string & json)
+{
+  const auto wasmStringStream = WasmStringStream::New();
+  wasmStringStream->SetJSON(json.c_str());
+  m_IStream = std::make_unique<std::stringstream>(std::move(wasmStringStream->GetStringStream()));
+}
+
+
+void
+InputStreamBase::SetFile(const std::string & fileName, const std::ios_base::openmode openMode)
+{
+  m_IStream = std::make_unique<std::ifstream>(fileName, openMode);
+}
+
+
+InputStreamBase::~InputStreamBase() = default;
+
 
 bool
 lexical_cast(const std::string & input, InputStreamBase & inputStream)