diff --git a/src/lib/urlHelper.js b/src/lib/urlHelper.js
index ac8d830d..0080c02f 100644
--- a/src/lib/urlHelper.js
+++ b/src/lib/urlHelper.js
@@ -23,35 +23,18 @@ export function getNewEntryUrl(collectionName, direct) {
  */
 const uriChars = /[\w\-.~]/i;
 const ucsChars = /[\xA0-\u{D7FF}\u{F900}-\u{FDCF}\u{FDF0}-\u{FFEF}\u{10000}-\u{1FFFD}\u{20000}-\u{2FFFD}\u{30000}-\u{3FFFD}\u{40000}-\u{4FFFD}\u{50000}-\u{5FFFD}\u{60000}-\u{6FFFD}\u{70000}-\u{7FFFD}\u{80000}-\u{8FFFD}\u{90000}-\u{9FFFD}\u{A0000}-\u{AFFFD}\u{B0000}-\u{BFFFD}\u{C0000}-\u{CFFFD}\u{D0000}-\u{DFFFD}\u{E1000}-\u{EFFFD}]/u;
+const validIRIChar = (char) => (uriChars.test(char) || ucsChars.test(char));
 // `sanitizeIRI` does not actually URI-encode the chars (that is the browser's and server's job), just removes the ones that are not allowed.
-function sanitizeIRI(str, { replacement = "" } = {}) {
+export function sanitizeIRI(str, { replacement = "" } = {}) {
   if (!isString(str)) throw "The input slug must be a string.";
   if (!isString(replacement)) throw "`options.replacement` must be a string.";
 
-  // This is where sanitization is actually done.
-  const sanitize = (input) => {
-    let result = "";
-    // We cannot use a `map` function here because `string.split()`
-    //   splits things like emojis into UTF-16 surrogate pairs,
-    //   and we want to use UTF-8 (it isn't required, but is nicer).
-    for (const char of input) {
-      if (uriChars.test(char) || ucsChars.test(char)) {
-        result += char;
-      } else {
-        result += replacement;
-      }
-    }
-    return result;
-  }
-
   // Check and make sure the replacement character is actually a safe char itself.
-  if (replacement !== "") {
-    const validReplacement = (sanitize(replacement) === replacement);
-    if (!validReplacement) throw "The replacement character(s) (options.replacement) is itself unsafe.";
-  }
+  if (!Array.from(replacement).every(validIRIChar)) throw "The replacement character(s) (options.replacement) is itself unsafe.";
 
-  // Actually do the sanitization.
-  return sanitize(str);
+  // `Array.from` must be used instead of `String.split` because
+  //   `split` converts things like emojis into UTF-16 surrogate pairs.
+  return Array.from(str).map(char => (validIRIChar(char) ? char : replacement)).join('');
 }
 
 export function sanitizeSlug(str, { replacement = '-' } = {}) {