diff --git a/src/options.js b/src/options.js
index 94ca533c1a..55f7709905 100644
--- a/src/options.js
+++ b/src/options.js
@@ -330,8 +330,10 @@ export function isTemporalString(values) {
 // coercion because we want to ignore false positives on e.g. empty strings.
 export function isNumericString(values) {
   for (const value of values) {
-    if (value == null || value === "") continue;
-    return typeof value === "string" && !isNaN(value);
+    if (value == null) continue;
+    if (typeof value !== "string") return false;
+    if (!value.trim()) continue;
+    return !isNaN(value);
   }
 }
 
diff --git a/test/options-test.js b/test/options-test.js
new file mode 100644
index 0000000000..55916478cc
--- /dev/null
+++ b/test/options-test.js
@@ -0,0 +1,46 @@
+import assert from "assert";
+import {isNumericString} from "../src/options.js";
+
+it("isNumericString detects numeric strings", () => {
+  assert.strictEqual(isNumericString(["42"]), true);
+});
+
+it("isNumericString doesn’t consider numbers to be strings", () => {
+  assert.strictEqual(isNumericString([42]), false);
+  assert.strictEqual(isNumericString([NaN]), false);
+});
+
+it("isNumericString doesn’t consider the string NaN to be numeric", () => {
+  assert.strictEqual(isNumericString(["NaN"]), false);
+});
+
+it("isNumericString ignores whitespace", () => {
+  assert.strictEqual(isNumericString([" 42"]), true);
+  assert.strictEqual(isNumericString(["42 "]), true);
+  assert.strictEqual(isNumericString([" 42 "]), true);
+});
+
+it("isNumericString ignores null", () => {
+  assert.strictEqual(isNumericString([null, "42", "notstring"]), true);
+  assert.strictEqual(isNumericString([null, "notstring", "42"]), false);
+});
+
+it("isNumericString ignores undefined", () => {
+  assert.strictEqual(isNumericString([undefined, "42", "notstring"]), true);
+  assert.strictEqual(isNumericString([undefined, "notstring", "42"]), false);
+});
+
+it("isNumericString ignores empty strings", () => {
+  assert.strictEqual(isNumericString(["", "42", "notstring"]), true);
+  assert.strictEqual(isNumericString(["", "notstring", "42"]), false);
+});
+
+it("isNumericString ignores whitespace strings", () => {
+  assert.strictEqual(isNumericString([" ", "42", "notstring"]), true);
+  assert.strictEqual(isNumericString([" ", "notstring", "42"]), false);
+});
+
+it("isNumericString only checks the first present value", () => {
+  assert.strictEqual(isNumericString(["42", "notstring"]), true);
+  assert.strictEqual(isNumericString(["notstring", "42"]), false);
+});