--- 
+++ 
@@ -19,6 +19,9 @@
     public Complex add(Complex rhs)
         throws NullArgumentException {
         MathUtils.checkNotNull(rhs);
+ if (isNaN() || rhs.isNaN()) {
+            return NaN;
+        }
         return createComplex(real + rhs.getReal(),
             imaginary + rhs.getImaginary());
     }