diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index ac4a2d4..c9bbfcf 100644
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -2115,7 +2115,7 @@
         fRadius = SkScalarToFloat(rad0);
         fDRadius = SkScalarToFloat(rad1) - fRadius;
 
-        fA = sqr(fDCenterX) - sqr(fDCenterY) - sqr(fDRadius);
+        fA = sqr(fDCenterX) + sqr(fDCenterY) - sqr(fDRadius);
         fRadius2 = sqr(fRadius);
         fRDR = fRadius * fDRadius;
     }