diff --git a/libvips/colour/sRGB2HSV.c b/libvips/colour/sRGB2HSV.c
index e45aa155..7a3c3b39 100644
--- a/libvips/colour/sRGB2HSV.c
+++ b/libvips/colour/sRGB2HSV.c
@@ -58,36 +58,36 @@ vips_sRGB2HSV_line( VipsColour *colour, VipsPel *out, VipsPel **in, int width )
 
 	float wrap_around_hue, secondary_diff;
 
-	#define RED		255.0f;
-	#define GREEN	85.0f;
-	#define BLUE	170.0f;
-
 
 	for( i = 0; i < width; i++ ) {
 
 		if (p[1] < p[2]) {
 			if (p[2] < p[0]) {
+				// Center red (at top)
 				c_max = p[0];
 				c_min = p[1];
 				secondary_diff = p[1] - p[2];
-				wrap_around_hue = RED;
+				wrap_around_hue = 255.0f;
 			} else {
+				// Center blue
 				c_max = p[2];
 				c_min = VIPS_MIN(p[1], p[0]);
 				secondary_diff = p[0] - p[1];
-				wrap_around_hue = BLUE;
+				wrap_around_hue = 170.0f;
 			}
 		} else {
 			if (p[1] < p[0]) {
+				// Center red (at bottom)
 				c_max = p[0];
 				c_min = p[2];
 				secondary_diff = p[1] - p[2];
 				wrap_around_hue = 0.0f;
 			} else {
+				// Center green
 				c_max = p[1];
 				c_min = VIPS_MIN(p[2], p[0]);
 				secondary_diff = p[2] - p[0];
-				wrap_around_hue = GREEN;
+				wrap_around_hue = 85.0f;
 			}
 		}