diff --git a/.changeset/neat-colts-impress.md b/.changeset/neat-colts-impress.md
new file mode 100644
index 0000000..1e6d46e
--- /dev/null
+++ b/.changeset/neat-colts-impress.md
@@ -0,0 +1,5 @@
+---
+'gatsby-plugin-use-dark-mode': patch
+---
+
+Ignore unexpected values in localStorage.
diff --git a/src/gatsby-node.ts b/src/gatsby-node.ts
index 5db2e46..8cb705e 100644
--- a/src/gatsby-node.ts
+++ b/src/gatsby-node.ts
@@ -86,19 +86,16 @@ function generateNoFlashScript({
       var preferDarkQuery = '(prefers-color-scheme: dark)';
       var mql = window.matchMedia(preferDarkQuery);
       var supportsColorSchemeQuery = mql.media === preferDarkQuery;
-      var localStorageTheme = null;
+      var localStorageValue = null;
       try {
-        localStorageTheme = localStorage.getItem(storageKey);
+        localStorageValue = JSON.parse(localStorage.getItem(storageKey));
       } catch (err) {}
-      var localStorageExists = localStorageTheme !== null;
-      if (localStorageExists) {
-        localStorageTheme = JSON.parse(localStorageTheme);
-      }
+      var isLocalStorageValueValid = localStorageValue === true || localStorageValue === false;
 
       // Determine the source of truth
-      if (localStorageExists) {
+      if (isLocalStorageValueValid) {
         // source of truth from localStorage
-        setClassOnDocumentBody(localStorageTheme);
+        setClassOnDocumentBody(localStorageValue);
       } else if (supportsColorSchemeQuery) {
         // source of truth from system
         setClassOnDocumentBody(mql.matches);