diff --git a/ChangeLog b/ChangeLog
index e93baba7..6d2481bd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -14,6 +14,7 @@
   are too unlike the main image
 - fix to vipsthumbnail --crop, thanks Alessandro 
 - add vips_sum()
+- add vips_hough()
 
 6/3/14 started 7.38.6
 - grey ramp minimum was wrong
diff --git a/libvips/arithmetic/hough.c b/libvips/arithmetic/hough.c
index 922fb10a..10820316 100644
--- a/libvips/arithmetic/hough.c
+++ b/libvips/arithmetic/hough.c
@@ -193,6 +193,10 @@ hough_vote( VipsHough *hough, VipsImage *accumulator, int x, int y )
 	}
 }
 
+/* See our superclass in statistic.c, but this is called for each section of
+ * each scanline. @x, @y is the position of the left end, @in is the pixel
+ * data, @n is the number of pixels in this scanline. VipsPel is uint8.
+ */
 static int
 vips_hough_scan( VipsStatistic *statistic, 
 	void *seq, int x, int y, void *in, int n )