diff --git a/include/IWriteFile.h b/include/IWriteFile.h
index ddc147df..68eac14a 100644
--- a/include/IWriteFile.h
+++ b/include/IWriteFile.h
@@ -21,7 +21,7 @@ namespace io
 		/** \param buffer Pointer to buffer of bytes to write.
 		\param sizeToWrite Amount of bytes to write to the file.
 		\return How much bytes were written. */
-		virtual s32 write(const void* buffer, u32 sizeToWrite) = 0;
+		virtual size_t write(const void* buffer, size_t sizeToWrite) = 0;
 
 		//! Changes position in file
 		/** \param finalPos Destination position in the file.
diff --git a/source/Irrlicht/CImageWriterBMP.cpp b/source/Irrlicht/CImageWriterBMP.cpp
index 682b3bf0..84f107ee 100644
--- a/source/Irrlicht/CImageWriterBMP.cpp
+++ b/source/Irrlicht/CImageWriterBMP.cpp
@@ -105,7 +105,7 @@ bool CImageWriterBMP::writeImage(io::IWriteFile* file, IImage* image, u32 param)
 	u32 row_stride = (pixel_size * imageHeader.Width);
 
 	// length of one row in bytes, rounded up to nearest 4-byte boundary
-	s32 row_size = ((3 * imageHeader.Width) + 3) & ~3;
+	size_t row_size = ((3 * imageHeader.Width) + 3) & ~3;
 
 	// allocate and clear memory for our scan line
 	u8* row_pointer = new u8[row_size];
diff --git a/source/Irrlicht/CImageWriterJPG.cpp b/source/Irrlicht/CImageWriterJPG.cpp
index d96011ad..55f1bc47 100644
--- a/source/Irrlicht/CImageWriterJPG.cpp
+++ b/source/Irrlicht/CImageWriterJPG.cpp
@@ -72,7 +72,7 @@ static boolean jpeg_empty_output_buffer(j_compress_ptr cinfo)
 static void jpeg_term_destination(j_compress_ptr cinfo)
 {
 	mem_dest_ptr dest = (mem_dest_ptr) cinfo->dest;
-	const s32 datacount = (s32)(OUTPUT_BUF_SIZE - dest->pub.free_in_buffer);
+	const size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
 	// for now just exit upon file error
 	if (dest->file->write(dest->buffer, datacount) != datacount)
 		ERREXIT (cinfo, JERR_FILE_WRITE);
diff --git a/source/Irrlicht/CImageWriterPPM.cpp b/source/Irrlicht/CImageWriterPPM.cpp
index aa821891..fd0db971 100644
--- a/source/Irrlicht/CImageWriterPPM.cpp
+++ b/source/Irrlicht/CImageWriterPPM.cpp
@@ -50,16 +50,22 @@ bool CImageWriterPPM::writeImage(io::IWriteFile *file, IImage *image, u32 param)
 		size = snprintf_irr(cache, 70, "P6\n");
 	else
 		size = snprintf_irr(cache, 70, "P3\n");
+	if ( size < 0 )
+		return false;
 
-	if (file->write(cache, size) != size)
+	if (file->write(cache, (size_t)size) != (size_t)size)
 		return false;
 
 	size = snprintf_irr(cache, 70, "%u %u\n", imageSize.Width, imageSize.Height);
-	if (file->write(cache, size) != size)
+	if ( size < 0 )
+		return false;
+	if (file->write(cache, (size_t)size) != (size_t)size)
 		return false;
 
 	size = snprintf_irr(cache, 70, "255\n");
-	if (file->write(cache, size) != size)
+	if ( size < 0 )
+		return false;
+	if (file->write(cache, (size_t)size) != (size_t)size)
 		return false;
 
 	if (binary)
@@ -88,7 +94,9 @@ bool CImageWriterPPM::writeImage(io::IWriteFile *file, IImage *image, u32 param)
 			{
 				const video::SColor& pixel = image->getPixel(c, h);
 				size = snprintf_irr(cache, 70, "%.3u %.3u %.3u%s", pixel.getRed(), pixel.getGreen(), pixel.getBlue(), n % 5 == 4 ? "\n" : "  ");
-				if (file->write(cache, size) != size)
+				if ( size < 0 )
+					return false;
+				if (file->write(cache, (size_t)size) != (size_t)size)
 					return false;
 			}
 		}
diff --git a/source/Irrlicht/CImageWriterTGA.cpp b/source/Irrlicht/CImageWriterTGA.cpp
index 229d2279..6198e3ff 100644
--- a/source/Irrlicht/CImageWriterTGA.cpp
+++ b/source/Irrlicht/CImageWriterTGA.cpp
@@ -108,7 +108,7 @@ bool CImageWriterTGA::writeImage(io::IWriteFile *file, IImage *image,u32 param)
 	u32 row_stride = (pixel_size * imageHeader.ImageWidth);
 
 	// length of one output row in bytes
-	s32 row_size = ((imageHeader.PixelDepth / 8) * imageHeader.ImageWidth);
+	size_t row_size = ((imageHeader.PixelDepth / 8) * imageHeader.ImageWidth);
 
 	// allocate a row do translate data into
 	u8* row_pointer = new u8[row_size];
diff --git a/source/Irrlicht/CMemoryFile.cpp b/source/Irrlicht/CMemoryFile.cpp
index 75a87d9e..22c57e65 100644
--- a/source/Irrlicht/CMemoryFile.cpp
+++ b/source/Irrlicht/CMemoryFile.cpp
@@ -107,9 +107,9 @@ CMemoryWriteFile::~CMemoryWriteFile()
 
 
 //! returns how much was written
-s32 CMemoryWriteFile::write(const void* buffer, u32 sizeToWrite)
+size_t CMemoryWriteFile::write(const void* buffer, size_t sizeToWrite)
 {
-	s32 amount = static_cast<s32>(sizeToWrite);
+	long amount = (long)sizeToWrite;
 	if (Pos + amount > Len)
 		amount -= Pos + amount - Len;
 
@@ -121,7 +121,7 @@ s32 CMemoryWriteFile::write(const void* buffer, u32 sizeToWrite)
 
 	Pos += amount;
 
-	return amount;
+	return (size_t)amount;
 }
 
 
diff --git a/source/Irrlicht/CMemoryFile.h b/source/Irrlicht/CMemoryFile.h
index dd132891..71f95057 100644
--- a/source/Irrlicht/CMemoryFile.h
+++ b/source/Irrlicht/CMemoryFile.h
@@ -66,7 +66,7 @@ namespace io
 		virtual ~CMemoryWriteFile();
 
 		//! returns how much was written
-		virtual s32 write(const void* buffer, u32 sizeToWrite) _IRR_OVERRIDE_;
+		virtual size_t write(const void* buffer, size_t sizeToWrite) _IRR_OVERRIDE_;
 
 		//! changes position in file, returns true if successful
 		virtual bool seek(long finalPos, bool relativeMovement = false) _IRR_OVERRIDE_;
diff --git a/source/Irrlicht/CWriteFile.cpp b/source/Irrlicht/CWriteFile.cpp
index 3036fc0c..657825e2 100644
--- a/source/Irrlicht/CWriteFile.cpp
+++ b/source/Irrlicht/CWriteFile.cpp
@@ -41,12 +41,12 @@ inline bool CWriteFile::isOpen() const
 
 
 //! returns how much was read
-s32 CWriteFile::write(const void* buffer, u32 sizeToWrite)
+size_t CWriteFile::write(const void* buffer, size_t sizeToWrite)
 {
 	if (!isOpen())
 		return 0;
 
-	return (s32)fwrite(buffer, 1, sizeToWrite, File);
+	return fwrite(buffer, 1, sizeToWrite, File);
 }
 
 
diff --git a/source/Irrlicht/CWriteFile.h b/source/Irrlicht/CWriteFile.h
index 54044fb8..d0e2c804 100644
--- a/source/Irrlicht/CWriteFile.h
+++ b/source/Irrlicht/CWriteFile.h
@@ -27,7 +27,7 @@ namespace io
 		virtual ~CWriteFile();
 
 		//! Reads an amount of bytes from the file.
-		virtual s32 write(const void* buffer, u32 sizeToWrite) _IRR_OVERRIDE_;
+		virtual size_t write(const void* buffer, size_t sizeToWrite) _IRR_OVERRIDE_;
 
 		//! Changes position in file, returns true if successful.
 		virtual bool seek(long finalPos, bool relativeMovement = false) _IRR_OVERRIDE_;
diff --git a/tests/writeImageToFile.cpp b/tests/writeImageToFile.cpp
index 22608ca7..4614befe 100644
--- a/tests/writeImageToFile.cpp
+++ b/tests/writeImageToFile.cpp
@@ -97,7 +97,7 @@ bool writeImageToFile(void)
 		goto cleanup;
 	}
 
-	if (memoryFile->getPos() != writtenFile->write(buffer, memoryFile->getPos()))
+	if ((size_t)memoryFile->getPos() != writtenFile->write(buffer, (size_t)memoryFile->getPos()))
 	{
 		logTestString("Error while writing to %s.\n", writtenFilename);
 		assert_log(false);
diff --git a/tools/GUIEditor/CMemoryReadWriteFile.cpp b/tools/GUIEditor/CMemoryReadWriteFile.cpp
index 6ccc8c7c..7a803e0d 100644
--- a/tools/GUIEditor/CMemoryReadWriteFile.cpp
+++ b/tools/GUIEditor/CMemoryReadWriteFile.cpp
@@ -13,7 +13,7 @@ CMemoryReadWriteFile::CMemoryReadWriteFile(const c8* filename)
 }
 
 
-s32 CMemoryReadWriteFile::write(const void* buffer, u32 sizeToWrite)
+size_t CMemoryReadWriteFile::write(const void* buffer, size_t sizeToWrite)
 {
 	// no point in writing 0 bytes
 	if (sizeToWrite < 1)
@@ -24,7 +24,7 @@ s32 CMemoryReadWriteFile::write(const void* buffer, u32 sizeToWrite)
 		Data.set_used(Pos+sizeToWrite);
 
 	// copy data
-	memcpy( (void*) &Data[Pos], buffer, (size_t) sizeToWrite);
+	memcpy( (void*) &Data[Pos], buffer, sizeToWrite);
 
 	Pos += sizeToWrite;
 
diff --git a/tools/GUIEditor/CMemoryReadWriteFile.h b/tools/GUIEditor/CMemoryReadWriteFile.h
index e8968f49..4b110bf9 100644
--- a/tools/GUIEditor/CMemoryReadWriteFile.h
+++ b/tools/GUIEditor/CMemoryReadWriteFile.h
@@ -27,7 +27,7 @@ namespace io
 		//! \param buffer: Pointer to buffer of bytes to write.
 		//! \param sizeToWrite: Amount of bytes to written to the file.
 		//! \return Returns how much bytes were written.
-		virtual s32 write(const void* buffer, u32 sizeToWrite);
+		virtual size_t write(const void* buffer, size_t sizeToWrite);
 
 		//! Changes position in file, returns true if successful.
 		//! \param finalPos: Destination position in the file.