diff --git a/Lib/patterns4.c b/Lib/patterns4.c
index 0c4a900..5afcc9a 100644
--- a/Lib/patterns4.c
+++ b/Lib/patterns4.c
@@ -23,6 +23,12 @@ int	x, y, v, delta;
 
 delta = high - low;
 
+if (0 == delta) {
+	fprintf(stderr, "%s: bad low/high parameters %d %d <- delta is 0\n",
+			__func__,			low, high);
+	return DIVISOR_IS_ZERO;
+	}
+
 for (x=0; x<dst->width; x++)
 	{
 	for (y=0; y<dst->height; y++)
@@ -44,6 +50,12 @@ int	x, y, r, g, b, delta;
 
 delta = high - low;
 
+if (0 == delta) {
+	fprintf(stderr, "%s: bad low/high parameters %d %d <- delta is 0\n",
+			__func__,			low, high);
+	return DIVISOR_IS_ZERO;
+	}
+
 for (x=0; x<dst->width; x++)
 	{
 	for (y=0; y<dst->height; y++)