diff --git a/CGAL_ImageIO/include/CGAL/ImageIO.h b/CGAL_ImageIO/include/CGAL/ImageIO.h
index c296b99aa39..47344adb747 100644
--- a/CGAL_ImageIO/include/CGAL/ImageIO.h
+++ b/CGAL_ImageIO/include/CGAL/ImageIO.h
@@ -516,7 +516,7 @@ CGAL_IMAGEIO_EXPORT char *ImageIO_gets( const _image *im, char *str, int size );
 
 /** replaces fseek function
  */
-CGAL_IMAGEIO_EXPORT int ImageIO_seek( const _image *im, long offset, int whence );
+CGAL_IMAGEIO_EXPORT long ImageIO_seek( const _image *im, long offset, int whence );
 
 /** replaces ferror function
  */
diff --git a/CGAL_ImageIO/include/CGAL/ImageIO_impl.h b/CGAL_ImageIO/include/CGAL/ImageIO_impl.h
index 31a7684aa3e..de4b743472b 100644
--- a/CGAL_ImageIO/include/CGAL/ImageIO_impl.h
+++ b/CGAL_ImageIO/include/CGAL/ImageIO_impl.h
@@ -111,6 +111,11 @@ void ImageIO_free(void *m) {
 
 
 
+unsigned int ImageIO_limit_len(size_t to_be_read)
+{
+  return (unsigned int)(std::min)(to_be_read, size_t(1u<<30));
+}
+
 /* mimics fwrite() function.
    According to _openWriteImage(), openMode will has one 
    of the following value:
@@ -120,6 +125,9 @@ void ImageIO_free(void *m) {
 */
 CGAL_INLINE_FUNCTION
 size_t ImageIO_write(const _image *im, const void *buf, size_t len) {
+  size_t to_be_written = len;
+  int l = -1;
+  char *b = (char*)buf;
 
   switch(im->openMode) {
   default :
@@ -127,23 +135,40 @@ size_t ImageIO_write(const _image *im, const void *buf, size_t len) {
     return 0;
   case OM_STD :
 #ifdef CGAL_USE_ZLIB
-    return gzwrite(im->fd, (void *) buf, len);
+    while ( (to_be_written > 0) && ((l = gzwrite(im->fd, (void *) b, ImageIO_limit_len(to_be_written))) > 0) ) {
+      to_be_written -= l;
+      b += l;
+    }
 #else 
-    return fwrite(buf, 1, len, im->fd);
+    while ( (to_be_written > 0) && ((l = fwrite( b, 1, ImageIO_limit_len(to_be_written), im->fd )) > 0) ) {
+      to_be_written -= l;
+      b += l;
+    }
 #endif
+    return ( len - to_be_written );
 #ifdef CGAL_USE_ZLIB
   case OM_GZ :
-    return gzwrite(im->fd, (void *) buf, len);
+    while ( (to_be_written > 0) && ((l = gzwrite(im->fd, (void *) b, ImageIO_limit_len(to_be_written))) > 0) ) {
+      to_be_written -= l;
+      b += l;
+    }
+    if(l<0)
+    {
+      int errnum;
+      fprintf(stderr, "zlib error: %s\n", gzerror(im->fd, &errnum));
+    }
+    return ( len - to_be_written );
+#else
+  case OM_FILE :
+    while ( (to_be_written > 0) && ((l = fwrite( b, 1, ImageIO_limit_len(to_be_written), im->fd )) > 0) ) {
+      to_be_written -= l;
+      b += l;
+    }
+    return ( len - to_be_written );
 #endif
-  case OM_FILE:
-    return fwrite(buf, 1, len, (FILE*)im->fd);
   }
-  //return 0;
-}
 
-size_t ImageIO_limit_read(size_t to_be_read)
-{
-  return (std::min)(to_be_read, size_t(1u<<30));
+  //return 0;
 }
 
 /* mimics fread() function.
@@ -165,12 +190,12 @@ size_t ImageIO_read(const _image *im, void *buf, size_t len)
     return 0;
   case OM_STD :
 #ifdef CGAL_USE_ZLIB
-    while ( (to_be_read > 0) && ((l = gzread(im->fd, (void *) b, ImageIO_limit_read(to_be_read))) > 0) ) {
+    while ( (to_be_read > 0) && ((l = gzread(im->fd, (void *) b, ImageIO_limit_len(to_be_read))) > 0) ) {
       to_be_read -= l;
       b += l;
     }
 #else 
-    while ( (to_be_read > 0) && ((l = fread( b, 1, ImageIO_limit_read(to_be_read), im->fd )) > 0) ) {
+    while ( (to_be_read > 0) && ((l = fread( b, 1, ImageIO_limit_len(to_be_read), im->fd )) > 0) ) {
       to_be_read -= l;
       b += l;
     }
@@ -178,7 +203,7 @@ size_t ImageIO_read(const _image *im, void *buf, size_t len)
     return ( len - to_be_read );
 #ifdef CGAL_USE_ZLIB
   case OM_GZ :
-    while ( (to_be_read > 0) && ((l = gzread(im->fd, (void *) b, ImageIO_limit_read(to_be_read))) > 0) ) {
+    while ( (to_be_read > 0) && ((l = gzread(im->fd, (void *) b, ImageIO_limit_len(to_be_read))) > 0) ) {
       to_be_read -= l;
       b += l;
     }
@@ -190,7 +215,7 @@ size_t ImageIO_read(const _image *im, void *buf, size_t len)
     return ( len - to_be_read );
 #else
   case OM_FILE :
-    while ( (to_be_read > 0) && ((l = fread( b, 1, ImageIO_limit_read(to_be_read), im->fd )) > 0) ) {
+    while ( (to_be_read > 0) && ((l = fread( b, 1, ImageIO_limit_len(to_be_read), im->fd )) > 0) ) {
       to_be_read -= l;
       b += l;
     }
@@ -240,7 +265,7 @@ char *ImageIO_gets( const _image *im, char *str, int size )
 
 
 CGAL_INLINE_FUNCTION
-int ImageIO_seek( const _image *im, long offset, int whence ) {
+long ImageIO_seek( const _image *im, long offset, int whence ) {
   switch(im->openMode) {
   case OM_CLOSE :
   default :
@@ -790,7 +815,7 @@ CGAL_INLINE_FUNCTION
 int _writeImage(_image *im, const char *name_to_be_written ) {
 
   int r = ImageIO_NO_ERROR;
-  int length = 0;
+  std::size_t length = 0;
   char *name = NULL;
   char *baseName = NULL;
 
@@ -814,7 +839,7 @@ int _writeImage(_image *im, const char *name_to_be_written ) {
   if ( name == NULL ) {
     im->imageFormat = InrimageFormat;
   } else {
-    int i,extLength;
+    std::size_t i,extLength;
     PTRIMAGE_FORMAT f;
     char ext[IMAGE_FORMAT_NAME_LENGTH];
     char *ptr;
@@ -1054,11 +1079,11 @@ static void _swapImageData( _image *im )
   unsigned char *ptr1, *ptr2, b[8];
   unsigned short int si, *ptr3, *ptr4;
   unsigned int        i, *ptr5, *ptr6;
-  int size, length;
+  std::size_t size, length;
   
   if( _getEndianness() != im->endianness) {
 
-    size = im->xdim * im->ydim * im->zdim * im->vdim * im->wdim;
+    size = std::size_t(im->xdim) * im->ydim * im->zdim * im->vdim * im->wdim;
     if ( size <= 0 ) return;
 
     length = size / im->wdim;
diff --git a/CGAL_ImageIO/include/CGAL/Image_3_impl.h b/CGAL_ImageIO/include/CGAL/Image_3_impl.h
index deeae53e950..fe07a2a0cf2 100644
--- a/CGAL_ImageIO/include/CGAL/Image_3_impl.h
+++ b/CGAL_ImageIO/include/CGAL/Image_3_impl.h
@@ -61,7 +61,7 @@ void Image_3::gl_draw(const float point_size,
   glColor3ub(r,g,b);
   glBegin(GL_POINTS);
   unsigned char *pData = (unsigned char*)image_ptr->data;
-  unsigned int xy = image_ptr->xdim * image_ptr->ydim;
+  std::size_t xy = image_ptr->xdim * image_ptr->ydim;
   for(unsigned int i=0;i<image_ptr->xdim;i+=5)
     for(unsigned int j=0;j<image_ptr->ydim;j+=5)
       for(unsigned int k=0;k<image_ptr->zdim;k+=5)
diff --git a/CGAL_ImageIO/src/CGAL_ImageIO/analyze_impl.h b/CGAL_ImageIO/src/CGAL_ImageIO/analyze_impl.h
index 4f923745450..2328ea36cba 100644
--- a/CGAL_ImageIO/src/CGAL_ImageIO/analyze_impl.h
+++ b/CGAL_ImageIO/src/CGAL_ImageIO/analyze_impl.h
@@ -790,9 +790,9 @@ writeAnalyzeHeader( const _image* im )
 /* Writes the given image body in an already opened file.*/
 CGAL_INLINE_FUNCTION
 int writeAnalyzeData(const _image *im) {
-  unsigned int lineSize = im->wdim * im->xdim * im->vdim ;
-  unsigned long size = lineSize * im->ydim * im->zdim;
-  unsigned int nwrt ;
+  std::size_t lineSize = std::size_t(im->wdim) * im->xdim * im->vdim ;
+  std::size_t size = lineSize * im->ydim * im->zdim;
+  std::size_t nwrt ;
 
   if(im->openMode != OM_CLOSE) {
 
diff --git a/CGAL_ImageIO/src/CGAL_ImageIO/gif_impl.h b/CGAL_ImageIO/src/CGAL_ImageIO/gif_impl.h
index ed9ac0b35d9..5545603d2cd 100644
--- a/CGAL_ImageIO/src/CGAL_ImageIO/gif_impl.h
+++ b/CGAL_ImageIO/src/CGAL_ImageIO/gif_impl.h
@@ -134,7 +134,7 @@ int   gif89 = 0;
   byte ch, ch1;
   byte *ptr, *ptr1;
   int i, block;
-  int npixels, maxpixels, aspect, filesize;
+  int npixels, maxpixels, aspect;
   float normaspect;
   int OutCount = 0,		/* Decompressor output 'stack count' */
     RWidth, RHeight,		/* screen dimensions */
@@ -186,7 +186,7 @@ int   gif89 = 0;
   }
   /* find the size of the file */
   fseek(fp, 0L, 2);
-  filesize = ftell(fp);
+  long filesize = ftell(fp);
   fseek(fp, 0L, 0);
 
  /* the +256's are so we can read truncated GIF files without fear of 
diff --git a/CGAL_ImageIO/src/CGAL_ImageIO/inr_impl.h b/CGAL_ImageIO/src/CGAL_ImageIO/inr_impl.h
index dc672626634..b53ea5a141d 100644
--- a/CGAL_ImageIO/src/CGAL_ImageIO/inr_impl.h
+++ b/CGAL_ImageIO/src/CGAL_ImageIO/inr_impl.h
@@ -75,7 +75,7 @@ static void concatStringElement(const stringListHead *strhead,
 /* Writes the given inrimage header in an already opened file.*/
 CGAL_INLINE_FUNCTION
 int _writeInrimageHeader(const _image *im, ENDIANNESS end) {
-  unsigned int pos, i;
+  std::size_t pos, i;
   char type[30], endianness[5], buf[257], scale[20];
   std::ostringstream oss;
 
diff --git a/CGAL_ImageIO/src/CGAL_ImageIO/pnm_impl.h b/CGAL_ImageIO/src/CGAL_ImageIO/pnm_impl.h
index 58c5a98ca34..6953b259c98 100644
--- a/CGAL_ImageIO/src/CGAL_ImageIO/pnm_impl.h
+++ b/CGAL_ImageIO/src/CGAL_ImageIO/pnm_impl.h
@@ -565,9 +565,9 @@ int writePgmImage(char *name,_image *im  )
   ImageIO_write( im, string, strlen( string ) );
 
   if ( im->dataMode == DM_ASCII ) {
-    int i, j, n, size;
+    std::size_t i, j, n, size;
     char *str = (char*)ImageIO_alloc( _LGTH_STRING_+1 );
-    size = im->xdim * im->ydim * im->zdim * im->vdim;
+    size = std::size_t(im->xdim) * im->ydim * im->zdim * im->vdim;
     n = ( im->xdim < 16 ) ? im->xdim : 16;
     i = 0;
     switch( im->wdim ) {
diff --git a/Installation/CMakeLists.txt b/Installation/CMakeLists.txt
index 32cb8508f6e..a8ec18de6bb 100644
--- a/Installation/CMakeLists.txt
+++ b/Installation/CMakeLists.txt
@@ -343,11 +343,11 @@ endif()
 #   CGAL-4.6   : 11.0.0 (int->size_t in CGAL_ImageIO)
 #   CGAL-4.7   : 11.0.1 (Nothing different in CGAL compiled libraries.)
 #   CGAL-4.8   : 11.0.2 (Nothing different in CGAL compiled libraries.)
-#   CGAL-4.9   : 11.0.3 (Nothing different in CGAL compiled libraries.)
+#   CGAL-4.9   : 12.0.0 (Change the API/ABI in CGAL_ImageIO, but issue with 4GB images.)
 # ¹) According to http://upstream-tracker.org/versions/cgal.html
 
-set( CGAL_SONAME_VERSION "11" )
-set( CGAL_SOVERSION      "11.0.3" )
+set( CGAL_SONAME_VERSION "12" )
+set( CGAL_SOVERSION      "12.0.0" )
 
 message( STATUS "CGAL_SONAME_VERSION=${CGAL_SONAME_VERSION}" )
 message( STATUS "CGAL_SOVERSION     =${CGAL_SOVERSION}" )