diff --git a/libtiff/tif_win32.c b/libtiff/tif_win32.c
index 088880e7..bf5fbfb3 100644
--- a/libtiff/tif_win32.c
+++ b/libtiff/tif_win32.c
@@ -27,34 +27,38 @@
  * Scott Wagner (wagner@itek.com), Itek Graphix, Rochester, NY USA
  */
 
-/*
-  CreateFileA/CreateFileW return type 'HANDLE'.
-
-  thandle_t is declared like
-
-    DECLARE_HANDLE(thandle_t);
-
-  in tiffio.h.
-
-  Windows (from winnt.h) DECLARE_HANDLE logic looks like
-
-  #ifdef STRICT
-    typedef void *HANDLE;
-  #define DECLARE_HANDLE(name) struct name##__ { int unused; }; typedef struct name##__ *name
-  #else
-    typedef PVOID HANDLE;
-  #define DECLARE_HANDLE(name) typedef HANDLE name
-  #endif
-
-  See http://bugzilla.maptools.org/show_bug.cgi?id=1941 for problems in WIN64
-  builds resulting from this.  Unfortunately, the proposed patch was lost.
-
-*/
-  
 #include "tiffiop.h"
 
 #include <windows.h>
 
+/*
+  CreateFileA/CreateFileW return type 'HANDLE' while TIFFFdOpen() takes 'int',
+  which is formally incompatible and can even seemingly be of different size:
+  HANDLE is 64 bit under Win64, while int is still 32 bits there.
+
+  However, only the lower 32 bits of a HANDLE are significant under Win64 as,
+  for interoperability reasons, they must have the same values in 32- and
+  64-bit programs running on the same system, see
+
+  https://docs.microsoft.com/en-us/windows/win32/winprog64/interprocess-communication
+
+  Because of this, it is safe to define the following trivial functions for
+  casting between ints and HANDLEs, which are only really needed to avoid
+  compiler warnings (and, perhaps, to make the code slightly more clear).
+  Note that using the intermediate cast to "intptr_t" is crucial for warning
+  avoidance, as this integer type has the same size as HANDLE in all builds.
+*/
+
+static inline thandle_t thandle_from_int(int ifd)
+{
+    return (thandle_t)(intptr_t)ifd;
+}
+
+static inline int thandle_to_int(thandle_t fd)
+{
+    return (int)(intptr_t)fd;
+}
+
 static tmsize_t
 _tiffReadProc(thandle_t fd, void* buf, tmsize_t size)
 {
@@ -237,7 +241,7 @@ TIFFFdOpen(int ifd, const char* name, const char* mode)
 			break;
 		}
 	}
-	tif = TIFFClientOpen(name, mode, (thandle_t)ifd, /* FIXME: WIN64 cast to pointer warning */
+	tif = TIFFClientOpen(name, mode, thandle_from_int(ifd),
 			_tiffReadProc, _tiffWriteProc,
 			_tiffSeekProc, _tiffCloseProc, _tiffSizeProc,
 			fSuppressMap ? _tiffDummyMapProc : _tiffMapProc,
@@ -282,7 +286,7 @@ TIFFOpen(const char* name, const char* mode)
 		return ((TIFF *)0);
 	}
 
-	tif = TIFFFdOpen((int)fd, name, mode);   /* FIXME: WIN64 cast from pointer to int warning */
+	tif = TIFFFdOpen(thandle_to_int(fd), name, mode);
 	if(!tif)
 		CloseHandle(fd);
 	return tif;
@@ -337,7 +341,7 @@ TIFFOpenW(const wchar_t* name, const char* mode)
 				    NULL, NULL);
 	}
 
-	tif = TIFFFdOpen((int)fd,    /* FIXME: WIN64 cast from pointer to int warning */
+	tif = TIFFFdOpen(thandle_to_int(fd),
 			 (mbname != NULL) ? mbname : "<unknown>", mode);
 	if(!tif)
 		CloseHandle(fd);