diff --git a/libtiff/tif_dir.c b/libtiff/tif_dir.c
index e90f14a0..51ffaafe 100644
--- a/libtiff/tif_dir.c
+++ b/libtiff/tif_dir.c
@@ -503,7 +503,17 @@ _TIFFVSetField(TIFF* tif, uint32_t tag, va_list ap)
 		 * for the image's codec then we'll arrive here.  This
 		 * happens, for example, when tiffcp is used to convert between
 		 * compression schemes and codec-specific tags are blindly copied.
+		 * 
+		 * This also happens when a FIELD_IGNORE tag is written.
 		 */
+		if (fip->field_bit == FIELD_IGNORE) {
+			TIFFErrorExt(tif->tif_clientdata, module,
+				"%s: Ignored %stag \"%s\" (not supported by libtiff)",
+				tif->tif_name, isPseudoTag(tag) ? "pseudo-" : "",
+				fip->field_name);
+			status = 0;
+			break;
+		}
 		if(fip->field_bit != FIELD_CUSTOM) {
 			TIFFErrorExt(tif->tif_clientdata, module,
 			    "%s: Invalid %stag \"%s\" (not supported by codec)",
diff --git a/libtiff/tif_dirinfo.c b/libtiff/tif_dirinfo.c
index 3371cb5c..b676ced8 100644
--- a/libtiff/tif_dirinfo.c
+++ b/libtiff/tif_dirinfo.c
@@ -64,15 +64,15 @@ static const TIFFFieldArray gpsFieldArray;
 static const TIFFField
 tiffFields[] = {
 	{ TIFFTAG_SUBFILETYPE, 1, 1, TIFF_LONG, 0, TIFF_SETGET_UINT32, TIFF_SETGET_UNDEFINED, FIELD_SUBFILETYPE, 1, 0, "SubfileType", NULL },
-	{ TIFFTAG_OSUBFILETYPE, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UNDEFINED, TIFF_SETGET_UNDEFINED, FIELD_SUBFILETYPE, 1, 0, "OldSubfileType", NULL },
+	{ TIFFTAG_OSUBFILETYPE, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UNDEFINED, TIFF_SETGET_UNDEFINED, FIELD_IGNORE, 1, 0, "OldSubfileType", NULL },
 	{ TIFFTAG_IMAGEWIDTH, 1, 1, TIFF_LONG, 0, TIFF_SETGET_UINT32, TIFF_SETGET_UNDEFINED, FIELD_IMAGEDIMENSIONS, 0, 0, "ImageWidth", NULL },
 	{ TIFFTAG_IMAGELENGTH, 1, 1, TIFF_LONG, 0, TIFF_SETGET_UINT32, TIFF_SETGET_UNDEFINED, FIELD_IMAGEDIMENSIONS, 1, 0, "ImageLength", NULL },
 	{ TIFFTAG_BITSPERSAMPLE, -1, -1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_BITSPERSAMPLE, 0, 0, "BitsPerSample", NULL },
 	{ TIFFTAG_COMPRESSION, -1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_COMPRESSION, 0, 0, "Compression", NULL },
 	{ TIFFTAG_PHOTOMETRIC, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_PHOTOMETRIC, 0, 0, "PhotometricInterpretation", NULL },
 	{ TIFFTAG_THRESHHOLDING, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_THRESHHOLDING, 1, 0, "Threshholding", NULL },
-	{ TIFFTAG_CELLWIDTH, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UNDEFINED, TIFF_SETGET_UNDEFINED, FIELD_IGNORE, 1, 0, "CellWidth", NULL },
-	{ TIFFTAG_CELLLENGTH, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UNDEFINED, TIFF_SETGET_UNDEFINED, FIELD_IGNORE, 1, 0, "CellLength", NULL },
+	{ TIFFTAG_CELLWIDTH, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_CUSTOM, 1, 0, "CellWidth", NULL },
+	{ TIFFTAG_CELLLENGTH, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_CUSTOM, 1, 0, "CellLength", NULL },
 	{ TIFFTAG_FILLORDER, 1, 1, TIFF_SHORT, 0, TIFF_SETGET_UINT16, TIFF_SETGET_UNDEFINED, FIELD_FILLORDER, 0, 0, "FillOrder", NULL },
 	{ TIFFTAG_DOCUMENTNAME, -1, -1, TIFF_ASCII, 0, TIFF_SETGET_ASCII, TIFF_SETGET_UNDEFINED, FIELD_CUSTOM, 1, 0, "DocumentName", NULL },
 	{ TIFFTAG_IMAGEDESCRIPTION, -1, -1, TIFF_ASCII, 0, TIFF_SETGET_ASCII, TIFF_SETGET_UNDEFINED, FIELD_CUSTOM, 1, 0, "ImageDescription", NULL },
diff --git a/libtiff/tif_dirread.c b/libtiff/tif_dirread.c
index 32653f04..4cf242b6 100644
--- a/libtiff/tif_dirread.c
+++ b/libtiff/tif_dirread.c
@@ -5386,6 +5386,9 @@ TIFFFetchNormalTag(TIFF* tif, TIFFDirEntry* dp, int recover)
 	switch (fip->set_field_type)
 	{
 		case TIFF_SETGET_UNDEFINED:
+				TIFFErrorExt(tif->tif_clientdata, "TIFFFetchNormalTag",
+					"Defined set_field_type of custom tag %"PRIu16" (%s) is TIFF_SETGET_UNDEFINED and thus tag is not read from file",
+					fip->field_tag, fip->field_name);
 			break;
 		case TIFF_SETGET_ASCII:
 			{