diff --git a/libtiff/tif_jpeg.c b/libtiff/tif_jpeg.c
index a967827..ec8485b 100644
--- a/libtiff/tif_jpeg.c
+++ b/libtiff/tif_jpeg.c
@@ -988,8 +988,15 @@ JPEGDecodeRaw(TIFF* tif, tidata_t buf, tsize_t cc, tsample_t s)
 	tsize_t nrows;
 	(void) s;
 
-	/* data is expected to be read in multiples of a scanline */
-	if ( (nrows = sp->cinfo.d.image_height) ) {
+    nrows = cc / sp->bytesperline;
+    if (cc % sp->bytesperline)
+		TIFFWarningExt(tif->tif_clientdata, tif->tif_name, "fractional scanline not read");
+
+    if( nrows > (int) sp->cinfo.d.image_height )
+        nrows = sp->cinfo.d.image_height;
+
+    /* data is expected to be read in multiples of a scanline */
+    if (nrows) {
 		/* Cb,Cr both have sampling factors 1, so this is correct */
 		JDIMENSION clumps_per_line = sp->cinfo.d.comp_info[1].downsampled_width;            
 		int samples_per_clump = sp->samplesperclump;
@@ -1087,8 +1094,7 @@ JPEGDecodeRaw(TIFF* tif, tidata_t buf, tsize_t cc, tsample_t s)
 			 * TODO: resolve this */
 			buf += sp->bytesperline;
 			cc -= sp->bytesperline;
-			nrows -= sp->v_sampling;
-		} while (nrows > 0);
+		} while (--nrows > 0);
 
 #ifdef JPEG_LIB_MK1
 		_TIFFfree(tmpbuf);
diff --git a/libtiff/tif_strip.c b/libtiff/tif_strip.c
index 63dec6b..b019b74 100644
--- a/libtiff/tif_strip.c
+++ b/libtiff/tif_strip.c
@@ -238,23 +238,19 @@ TIFFScanlineSize(TIFF* tif)
 				     ycbcrsubsampling + 0,
 				     ycbcrsubsampling + 1);
 
-			if (ycbcrsubsampling[0] == 0) {
+			if (ycbcrsubsampling[0]*ycbcrsubsampling[1] == 0) {
 				TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
 					     "Invalid YCbCr subsampling");
 				return 0;
 			}
 
-			scanline = TIFFroundup(td->td_imagewidth,
+			/* number of sample clumps per line */
+			scanline = TIFFhowmany(td->td_imagewidth,
 					       ycbcrsubsampling[0]);
-			scanline = TIFFhowmany8(multiply(tif, scanline,
-							 td->td_bitspersample,
-							 "TIFFScanlineSize"));
-			return ((tsize_t)
-				summarize(tif, scanline,
-					  multiply(tif, 2,
-						scanline / ycbcrsubsampling[0],
-						"TIFFVStripSize"),
-					  "TIFFVStripSize"));
+			/* number of samples per line */
+			scanline = multiply(tif, scanline,
+					    ycbcrsubsampling[0]*ycbcrsubsampling[1] + 2,
+					    "TIFFScanlineSize");
 		} else {
 			scanline = multiply(tif, td->td_imagewidth,
 					    td->td_samplesperpixel,