diff --git a/src/index.ts b/src/index.ts
index ede2c4d..4163a69 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -20,10 +20,20 @@ export function persistResumableFields(id: string, options?: PersistOptions): vo
     }
   }
 
-  const fields = resumables.filter(field => shouldResumeField(field)).map(field => [field.id, field.value])
+  let fields = resumables.filter(field => shouldResumeField(field)).map(field => [field.id, field.value])
 
   if (fields.length) {
     try {
+      const previouslyStoredFieldsJson = sessionStorage.getItem(key)
+
+      if (previouslyStoredFieldsJson !== null) {
+        const previouslyStoredFields: string[][] = JSON.parse(previouslyStoredFieldsJson)
+        const fieldsNotReplaced: string[][] = previouslyStoredFields.filter(function (oldField) {
+          return !fields.some(field => field[0] === oldField[0])
+        })
+        fields = fields.concat(fieldsNotReplaced)
+      }
+
       sessionStorage.setItem(key, JSON.stringify(fields))
     } catch {
       // Ignore browser private mode error.
@@ -46,13 +56,8 @@ export function restoreResumableFields(id: string, options?: RestoreOptions): vo
 
   if (!fields) return
 
-  try {
-    sessionStorage.removeItem(key)
-  } catch {
-    // Ignore browser private mode error.
-  }
-
   const changedFields: Array<HTMLInputElement | HTMLTextAreaElement> = []
+  const storedFieldsNotFound: string[][] = []
 
   for (const [fieldId, value] of JSON.parse(fields)) {
     const resumeEvent = new CustomEvent('session:resume', {
@@ -63,17 +68,30 @@ export function restoreResumableFields(id: string, options?: RestoreOptions): vo
 
     if (document.dispatchEvent(resumeEvent)) {
       const field = document.getElementById(fieldId)
-      if (
-        field &&
-        (field instanceof HTMLInputElement || field instanceof HTMLTextAreaElement) &&
-        field.value === field.defaultValue
-      ) {
-        field.value = value
-        changedFields.push(field)
+      if (field && (field instanceof HTMLInputElement || field instanceof HTMLTextAreaElement)) {
+        if (field.value === field.defaultValue) {
+          field.value = value
+          changedFields.push(field)
+        }
+      } else {
+        storedFieldsNotFound.push([fieldId, value])
       }
     }
   }
 
+  // Some fields we want to restore are not always immediately present in the
+  // DOM and may be added later. This holds onto the values until
+  // they're needed.
+  if (storedFieldsNotFound.length === 0) {
+    try {
+      sessionStorage.removeItem(key)
+    } catch {
+      // Ignore browser private mode error.
+    }
+  } else {
+    sessionStorage.setItem(key, JSON.stringify(storedFieldsNotFound))
+  }
+
   setTimeout(function () {
     for (const el of changedFields) {
       el.dispatchEvent(new CustomEvent('change', {bubbles: true, cancelable: true}))
diff --git a/test/test.js b/test/test.js
index 9e39ce8..150ff5c 100644
--- a/test/test.js
+++ b/test/test.js
@@ -20,6 +20,38 @@ describe('session-resume', function () {
       assert.equal(document.querySelector('#my-second-field').value, 'second-field-value')
     })
 
+    it('leaves unrestored values in session storage', function () {
+      sessionStorage.setItem(
+        'session-resume:test-persist',
+        JSON.stringify([
+          ['my-first-field', 'test2'],
+          ['non-existant-field', 'test3']
+        ])
+      )
+      document.querySelector('#my-first-field').value = 'first-field-value'
+      document.querySelector('#my-second-field').value = 'second-field-value'
+
+      restoreResumableFields('test-persist')
+
+      assert.equal(document.querySelector('#my-first-field').value, 'test2')
+      assert.equal(document.querySelector('#my-second-field').value, 'second-field-value')
+
+      // Some fields we want to restore are not always present in the DOM
+      // and may be added later. We hold onto the values until they're needed.
+      assert.deepEqual(JSON.parse(sessionStorage.getItem('session-resume:test-persist')), [
+        ['non-existant-field', 'test3']
+      ])
+    })
+
+    it('removes the sessionStore key when all the fields were found', function () {
+      sessionStorage.setItem('session-resume:test-persist', JSON.stringify([['my-first-field', 'test2']]))
+      restoreResumableFields('test-persist')
+
+      // Some fields we want to restore are not always present in the DOM
+      // and may be added later. We hold onto the values until they're needed.
+      assert.equal(sessionStorage.getItem('session-resume:test-persist'), null)
+    })
+
     it('fires off session:resume events for changed fields', function () {
       const fieldsRestored = {}
       document.addEventListener('session:resume', function (event) {
@@ -55,5 +87,32 @@ describe('session-resume', function () {
         ['my-second-field', 'test2']
       ])
     })
+
+    it('holds onto existing values in the store', function () {
+      sessionStorage.setItem('session-resume:test-persist', JSON.stringify([['non-existant-field', 'test3']]))
+      document.querySelector('#my-first-field').value = 'test1'
+      document.querySelector('#my-second-field').value = 'test2'
+
+      persistResumableFields('test-persist')
+
+      assert.deepEqual(JSON.parse(sessionStorage.getItem('session-resume:test-persist')), [
+        ['my-first-field', 'test1'],
+        ['my-second-field', 'test2'],
+        ['non-existant-field', 'test3']
+      ])
+    })
+
+    it('replaces old values with the latest field values', function () {
+      sessionStorage.setItem('session-resume:test-persist', JSON.stringify([['my-first-field', 'old data']]))
+      document.querySelector('#my-first-field').value = 'test1'
+      document.querySelector('#my-second-field').value = 'test2'
+
+      persistResumableFields('test-persist')
+
+      assert.deepEqual(JSON.parse(sessionStorage.getItem('session-resume:test-persist')), [
+        ['my-first-field', 'test1'],
+        ['my-second-field', 'test2']
+      ])
+    })
   })
 })