diff --git a/experimental/Intersection/CubicUtilities.cpp b/experimental/Intersection/CubicUtilities.cpp
index 70f10c1..a5174c9 100644
--- a/experimental/Intersection/CubicUtilities.cpp
+++ b/experimental/Intersection/CubicUtilities.cpp
@@ -115,7 +115,9 @@
     if (approximately_zero(A)) {  // we're just a quadratic
         return quadraticRootsReal(B, C, D, s);
     }
-    if (approximately_zero(D)) { // 0 is one root
+    if (approximately_zero_when_compared_to(D, A)
+            && approximately_zero_when_compared_to(D, B)
+            && approximately_zero_when_compared_to(D, C)) { // 0 is one root
         int num = quadraticRootsReal(A, B, C, s);
         for (int i = 0; i < num; ++i) {
             if (approximately_zero(s[i])) {
@@ -231,7 +233,6 @@
     dxdy.y = derivativeAtT(&cubic[0].y, t);
 }
 
-
 int find_cubic_inflections(const Cubic& src, double tValues[])
 {
     double Ax = src[1].x - src[0].x;