diff --git a/src/distPlus/distribution/AlgebraicShapeCombination.re b/src/distPlus/distribution/AlgebraicShapeCombination.re
index c12e96c7..edcf00ad 100644
--- a/src/distPlus/distribution/AlgebraicShapeCombination.re
+++ b/src/distPlus/distribution/AlgebraicShapeCombination.re
@@ -209,30 +209,9 @@ let toDiscretePointMassesFromDiscrete = (s: DistTypes.xyShape): pointMassesWithM
   let {xs, ys}: XYShape.T.t = s;
   let n = E.A.length(xs);
 
-  let masses: array(float) = Belt.Array.makeUninitializedUnsafe(n); // doesn't include the fake first and last points
-  let means: array(float) = Belt.Array.makeUninitializedUnsafe(n);
-  let variances: array(float) = Belt.Array.makeUninitializedUnsafe(n);
-
-  for (i in 0 to n - 1) {
-    Belt.Array.set(
-      masses,
-      i,
-      ys[i]
-    ) |> ignore;
-
-    Belt.Array.set(
-      means,
-      i,
-      xs[i]
-    ) |> ignore;
-
-    Belt.Array.set(
-      variances,
-      i,
-      0.0
-    ) |> ignore;
-    ();
-  };
+  let masses: array(float) = Belt.Array.makeBy(n, i => ys[i]);
+  let means: array(float) = Belt.Array.makeBy(n, i => xs[i]);
+  let variances: array(float) = Belt.Array.makeBy(n, i => 0.0);
 
   {n, masses, means, variances};
 };
diff --git a/src/distPlus/distribution/Continuous.re b/src/distPlus/distribution/Continuous.re
index 939c88aa..1adb60c0 100644
--- a/src/distPlus/distribution/Continuous.re
+++ b/src/distPlus/distribution/Continuous.re
@@ -41,7 +41,7 @@ let combinePointwise =
     (
       ~integralSumCachesFn=(_, _) => None,
       ~integralCachesFn: (t, t) => option(t) =(_, _) => None,
-      ~extrapolation=`UseZero,
+      ~distributionType: DistTypes.distributionType = `PDF,
       fn: (float, float) => float,
       t1: DistTypes.continuousShape,
       t2: DistTypes.continuousShape,
@@ -68,6 +68,11 @@ let combinePointwise =
   | (`Stepwise, `Linear) => (stepwiseToLinear(t1), t2);
   };
 
+  let extrapolation = switch (distributionType) {
+  | `PDF => `UseZero
+  | `CDF => `UseOutermostPoints
+  };
+
   let interpolator = XYShape.XtoY.continuousInterpolator(t1.interpolation, extrapolation);
 
   make(
diff --git a/src/distPlus/distribution/DistTypes.re b/src/distPlus/distribution/DistTypes.re
index 62afdc22..92f03ee6 100644
--- a/src/distPlus/distribution/DistTypes.re
+++ b/src/distPlus/distribution/DistTypes.re
@@ -9,6 +9,11 @@ type domain =
   | RightLimited(domainLimit)
   | LeftAndRightLimited(domainLimit, domainLimit);
 
+type distributionType = [
+  | `PDF
+  | `CDF
+];
+
 type xyShape = {
   xs: array(float),
   ys: array(float),
diff --git a/src/distPlus/expressionTree/ExpressionTreeEvaluator.re b/src/distPlus/expressionTree/ExpressionTreeEvaluator.re
index 0af87e56..0a4b7070 100644
--- a/src/distPlus/expressionTree/ExpressionTreeEvaluator.re
+++ b/src/distPlus/expressionTree/ExpressionTreeEvaluator.re
@@ -131,7 +131,7 @@ module PointwiseCombination = {
         `RenderedDist(
           Shape.combinePointwise(
             ~integralSumCachesFn=(a, b) => Some(a +. b),
-            ~integralCachesFn=(a, b) => Some(Continuous.combinePointwise(~extrapolation=`UseOutermostPoints, (+.), a, b)),
+            ~integralCachesFn=(a, b) => Some(Continuous.combinePointwise(~distributionType=`CDF, (+.), a, b)),
             (+.),
             rs1,
             rs2,