diff --git a/tests/Monad.hs b/tests/Monad.hs
index 03e93902..e2b8bd87 100644
--- a/tests/Monad.hs
+++ b/tests/Monad.hs
@@ -22,6 +22,8 @@ prop_sampleM df = monadic' $ do
     let finalRowCount = D.nRows finalDf
     let realRate = roundToTwoPlaces $ fromIntegral finalRowCount / fromIntegral rowCount
     let diff = abs $ expectedRate - realRate
-    assert (diff <= 0.11)
+    -- calculates the 99.99% confidence interval (quickcheck runs 100 tests, aim for 1/10000)
+    let tolerance = 3.89 * sqrt (expectedRate * (1 - expectedRate) / fromIntegral rowCount)
+    assert (diff <= tolerance)
 
 tests = [prop_sampleM]