diff --git a/ChangeLog b/ChangeLog
index 447c3333..4e05a2e8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,6 +4,7 @@
   overlap now matches the openslide writer
 - wrap VipsInterpolate for C++
 - so affinei and affinei_all appear in Python
+- be more cautious enabling YCbCr mode in tiff write
 
 20/7/12 started 7.30.0
 - support "rs" mode in vips7
diff --git a/libvips/foreign/vips2tiff.c b/libvips/foreign/vips2tiff.c
index 55d17e7b..d383412e 100644
--- a/libvips/foreign/vips2tiff.c
+++ b/libvips/foreign/vips2tiff.c
@@ -131,6 +131,8 @@
  * 2/6/12
  * 	- copy jpeg pyramid in gather in RGB mode ... tiff4 doesn't do ycbcr
  * 	  mode
+ * 7/8/12
+ * 	- be more cautious enabling YCbCr mode
  */
 
 /*
@@ -458,15 +460,9 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
 	TIFFSetField( tif, TIFFTAG_ORIENTATION, ORIENTATION_TOPLEFT );
 	TIFFSetField( tif, TIFFTAG_COMPRESSION, tw->compression );
 
-	if( tw->compression == COMPRESSION_JPEG ) {
+	if( tw->compression == COMPRESSION_JPEG ) 
 		TIFFSetField( tif, TIFFTAG_JPEGQUALITY, tw->jpqual );
 
-		/* Enable rgb->ycbcr conversion in the jpeg write. See also
-		 * the photometric selection below.
-		 */
-		TIFFSetField( tif, TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
-	}
-
 	if( tw->predictor != VIPS_FOREIGN_TIFF_PREDICTOR_NONE ) 
 		TIFFSetField( tif, TIFFTAG_PREDICTOR, tw->predictor );
 
@@ -515,6 +511,9 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
 
 		case 3:
 		case 4:
+			/* could be: RGB, RGBA, CMYK, LAB, LABA, generic
+			 * multi-band image.
+			 */
 			if( tw->im->Type == VIPS_INTERPRETATION_LAB || 
 				tw->im->Type == VIPS_INTERPRETATION_LABS ) 
 				photometric = PHOTOMETRIC_CIELAB;
@@ -524,12 +523,16 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
 					TIFFTAG_INKSET, INKSET_CMYK );
 			}
 			else if( tw->compression == COMPRESSION_JPEG &&
-				tw->im->Bands == 3 ) 
+				tw->im->Bands == 3 &&
+				tw->im->BandFmt == VIPS_FORMAT_UCHAR ) { 
 				/* This signals to libjpeg that it can do
 				 * YCbCr chrominance subsampling from RGB, not
 				 * that we will supply the image as YCbCr.
 				 */
 				photometric = PHOTOMETRIC_YCBCR;
+				TIFFSetField( tif, TIFFTAG_JPEGCOLORMODE, 
+					JPEGCOLORMODE_RGB );
+			}
 			else
 				photometric = PHOTOMETRIC_RGB;
 
@@ -538,9 +541,12 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
 				v[0] = EXTRASAMPLE_ASSOCALPHA;
 				TIFFSetField( tif, TIFFTAG_EXTRASAMPLES, 1, v );
 			}
+
 			break;
 
 		case 5:
+			/* Only CMYKA
+			 */
 			if( tw->im->Type == VIPS_INTERPRETATION_CMYK ) {
 				photometric = PHOTOMETRIC_SEPARATED;
 				TIFFSetField( tif, 
@@ -1358,16 +1364,22 @@ tiff_copy( TiffWrite *tw, TIFF *out, TIFF *in )
 	if( tw->compression == COMPRESSION_JPEG ) {
 		TIFFSetField( out, TIFFTAG_JPEGQUALITY, tw->jpqual );
 
-		/* Enable rgb->ycbcr conversion in the jpeg write. See also
-		 * the photometric selection below.
+		/* Only for three-band, 8-bit images.
 		 */
-		TIFFSetField( out, TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
+		if( tw->im->Bands == 3 &&
+			tw->im->BandFmt == VIPS_FORMAT_UCHAR ) { 
+			/* Enable rgb->ycbcr conversion in the jpeg write. 
+			 */
+			TIFFSetField( out, 
+				TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
 
-		/* And we want ycbcr expanded to rgb on read. Otherwise
-		 * TIFFTileSize() will give us the size of a chrominance
-		 * subsampled tile.
-		 */
-		TIFFSetField( in, TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
+			/* And we want ycbcr expanded to rgb on read. Otherwise
+			 * TIFFTileSize() will give us the size of a chrominance
+			 * subsampled tile.
+			 */
+			TIFFSetField( in, 
+				TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
+		}
 	}
 
 	/* We can't copy profiles :( Set again from TiffWrite.