diff --git a/TODO b/TODO
index a872abeb..e4e24aca 100644
--- a/TODO
+++ b/TODO
@@ -1,16 +1,3 @@
-- try:
-
-	$ vips im_copy babe.jpg babe.tif:lzw,tile,,manybit,res_inch:72.00x72.00,,
-	$ header -a babe.tif
-	babe.tif: 1024x768 uchar, 3 bands, srgb VipsImage (0x2225050)
-	xres: 7.200000
-	yres: 7.200000
-	resolution-unit: in
-
-  argh!
-
-
-
 blocking bugs
 =============
 
diff --git a/libvips/deprecated/im_vips2tiff.c b/libvips/deprecated/im_vips2tiff.c
index 8577093f..05caf3cf 100644
--- a/libvips/deprecated/im_vips2tiff.c
+++ b/libvips/deprecated/im_vips2tiff.c
@@ -178,20 +178,10 @@ im_vips2tiff( IMAGE *in, const char *filename )
 	}
 
 	if( (q = im_getnextoption( &p )) ) {
-		if( im_isprefix( "res_cm", q ) ) {
-			if( resunit == VIPS_FOREIGN_TIFF_RESUNIT_INCH ) {
-				xres /= 2.54;
-				yres /= 2.54;
-			}
+		if( im_isprefix( "res_cm", q ) ) 
 			resunit = VIPS_FOREIGN_TIFF_RESUNIT_CM;
-		}
-		else if( im_isprefix( "res_inch", q ) ) {
-			if( resunit == VIPS_FOREIGN_TIFF_RESUNIT_CM ) {
-				xres *= 2.54;
-				yres *= 2.54;
-			}
+		else if( im_isprefix( "res_inch", q ) ) 
 			resunit = VIPS_FOREIGN_TIFF_RESUNIT_INCH;
-		}
 		else {
 			im_error( "im_vips2tiff", _( "unknown resolution unit "
 				"\"%s\"\nshould be one of \"res_cm\" or "
@@ -209,6 +199,15 @@ im_vips2tiff( IMAGE *in, const char *filename )
 
 				yres = xres;
 			}
+
+			/* vips resolutions are always in pixels/mm. If the
+			 * user specifies ",res_inch:72x72" then they are
+			 * using pixels/inch instead and we must convert.
+			 */
+			if( resunit == VIPS_FOREIGN_TIFF_RESUNIT_INCH ) {
+				xres /= 2.54;
+				yres /= 2.54;
+			}
 		}
 	}
 
diff --git a/libvips/foreign/foreign.c b/libvips/foreign/foreign.c
index ea5aead2..3eafd96c 100644
--- a/libvips/foreign/foreign.c
+++ b/libvips/foreign/foreign.c
@@ -1715,9 +1715,9 @@ vips_tiffload( const char *filename, VipsImage **out, ... )
  * @tile_height; set tile size
  * @pyramid; set %TRUE to write an image pyramid
  * @squash; squash 8-bit images down to 1 bit
- * @resunit; use pixels per inch or cm for the resolution
- * @xres; horizontal resolution
- * @yres; vertical resolution
+ * @resunit; convert resolution to pixels per inch or cm during write
+ * @xres; horizontal resolution in pixels/mm
+ * @yres; vertical resolution in pixels/mm
  * @bigtiff; write a BigTiff file
  *
  * Write a VIPS image to a file as TIFF.
@@ -1767,6 +1767,7 @@ vips_tiffload( const char *filename, VipsImage **out, ... )
  *
  * Use @xres and @yres to override the default horizontal and vertical
  * resolutions. By default these values are taken from the VIPS image header. 
+ * libvips resolution is always in pixels per millimetre.
  *
  * Set @bigtiff to attempt to write a bigtiff. 
  * Bigtiff is a variant of the TIFF