diff --git a/test/propeller/tools/calculus_test.cljc b/test/propeller/tools/calculus_test.cljc
index bec84f1..6300479 100644
--- a/test/propeller/tools/calculus_test.cljc
+++ b/test/propeller/tools/calculus_test.cljc
@@ -3,6 +3,7 @@
             [propeller.tools.calculus :as c]))
 (t/deftest deriv_test
   (t/is (letfn [(cubic [x] (let [a (double x)] (* a a a)))]
-         (=  (c/deriv (cubic 2)) 2.0))
+          (< (max (- (c/deriv cubic 2) 12) (- (- (c/deriv cubic 2) 12))) 0.001)
+          )
         )
   )