function normalizeBasis(basis) {
   return {
     mapIndex(I, S, T) {
-      const b = +basis(I, S);
+      const b = Number(basis(I, S));
       for (const i of I) {
-        T[i] = S[i] === null ? NaN : S[i] / b;
+        T[i] = S[i] === null ? NaN : Number(S[i]) / b;
       }
     }
   };

 function normalizeBasis(basis) {
   return {
     mapIndex(I, S, T) {
+      S = S.map(Number);
       const b = +basis(I, S);
       for (const i of I) {
         T[i] = S[i] === null ? NaN : S[i] / b;

--- a/src/options.js
+++ b/src/options.js
@@ -54,7 +54,7 @@ function maybeTypedMap(data, f, type) {
   return map(data, isNumberType(type) ? (d, i) => coerceNumber(f(d, i)) : f, type); // allow conversion from BigInt
 }

-function maybeTypedArrayify(data, type) {
+export function maybeTypedArrayify(data, type) {
   return type === undefined
     ? arrayify(data) // preserve undefined type
     : isArrowVector(data)
diff --git a/src/transforms/normalize.js b/src/transforms/normalize.js
index f4d225cd..2f426020 100644
--- a/src/transforms/normalize.js
+++ b/src/transforms/normalize.js
@@ -1,6 +1,6 @@
 import {extent, deviation, max, mean, median, min, sum} from "d3";
 import {defined} from "../defined.js";
-import {percentile, taker} from "../options.js";
+import {maybeTypedArrayify, percentile, taker} from "../options.js";
 import {mapX, mapY} from "./map.js";

 export function normalizeX(basis, options) {
@@ -43,6 +43,7 @@ export function normalize(basis) {
 function normalizeBasis(basis) {
   return {
     mapIndex(I, S, T) {
+      S = maybeTypedArrayify(S, Float64Array);
       const b = +basis(I, S);
       for (const i of I) {
         T[i] = S[i] === null ? NaN : S[i] / b;