diff --git a/src/shared/color-util.c b/src/shared/color-util.c
index 776445ecfc..9d714c0fff 100644
--- a/src/shared/color-util.c
+++ b/src/shared/color-util.c
@@ -11,35 +11,38 @@ void rgb_to_hsv(double r, double g, double b,
         assert(r >= 0 && r <= 1);
         assert(g >= 0 && g <= 1);
         assert(b >= 0 && b <= 1);
-        assert(ret_h);
-        assert(ret_s);
-        assert(ret_v);
 
         double max_color = fmax(r, fmax(g, b));
         double min_color = fmin(r, fmin(g, b));
         double delta = max_color - min_color;
 
-        *ret_v = max_color * 100.0;
+        if (ret_v)
+                *ret_v = max_color * 100.0;
 
-        if (max_color > 0)
-                *ret_s = delta / max_color * 100.0;
-        else {
-                *ret_s = 0;
-                *ret_h = NAN;
+        if (max_color <= 0) {
+                if (ret_s)
+                        *ret_s = 0;
+                if (ret_h)
+                        *ret_h = NAN;
                 return;
         }
 
-        if (delta > 0) {
-                if (r >= max_color)
-                        *ret_h = 60 * fmod((g - b) / delta, 6);
-                else if (g >= max_color)
-                        *ret_h = 60 * (((b - r) / delta) + 2);
-                else if (b >= max_color)
-                        *ret_h = 60 * (((r - g) / delta) + 4);
+        if (ret_s)
+                *ret_s = delta / max_color * 100.0;
 
-                *ret_h = fmod(*ret_h, 360);
-        } else
-                *ret_h = NAN;
+        if (ret_h) {
+                if (delta > 0) {
+                        if (r >= max_color)
+                                *ret_h = 60 * fmod((g - b) / delta, 6);
+                        else if (g >= max_color)
+                                *ret_h = 60 * (((b - r) / delta) + 2);
+                        else if (b >= max_color)
+                                *ret_h = 60 * (((r - g) / delta) + 4);
+
+                        *ret_h = fmod(*ret_h, 360);
+                } else
+                        *ret_h = NAN;
+        }
 }
 
 void hsv_to_rgb(double h, double s, double v,