diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0117701b..9fa8aaff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- `replaceCustomValues()` only replacing element submission data that is a string
+
 ## [0.2.4] - 2021-11-15
 
 ### Fixed
diff --git a/src/replaceCustomValues.ts b/src/replaceCustomValues.ts
index 5f3c907e..c919e260 100644
--- a/src/replaceCustomValues.ts
+++ b/src/replaceCustomValues.ts
@@ -81,7 +81,7 @@ export function getElementSubmissionValue({
   formatTime: (value: string) => string
   formatNumber: (value: number) => string
   formatCurrency: (value: number) => string
-}): string | undefined | Array<string> {
+}): unknown {
   const formElement = findFormElement(
     form.elements,
     (element) =>
@@ -212,7 +212,10 @@ function replaceElementValues(
       formatCurrency,
     })
 
-    return newString.replace(match, typeof value === 'string' ? value : '')
+    return newString.replace(
+      match,
+      value === undefined ? '' : (value as string),
+    )
   }, text)
 }