diff --git a/.changes/window-label-unique.md b/.changes/window-label-unique.md
new file mode 100644
index 000000000..27aa3f6ca
--- /dev/null
+++ b/.changes/window-label-unique.md
@@ -0,0 +1,5 @@
+---
+"tauri": patch
+---
+
+Enfore uniqueness of window label.
diff --git a/core/tauri/src/error.rs b/core/tauri/src/error.rs
index 43fbcdb6b..8926e4014 100644
--- a/core/tauri/src/error.rs
+++ b/core/tauri/src/error.rs
@@ -17,6 +17,9 @@ pub enum Error {
   /// Failed to create window.
   #[error("failed to create window")]
   CreateWindow,
+  /// Window label must be unique.
+  #[error("a window with label `{0}` already exists")]
+  WindowLabelAlreadyExists(String),
   /// Can't access webview dispatcher because the webview was closed or not found.
   #[error("webview not found: invalid label or it was closed")]
   WebviewNotFound,
diff --git a/core/tauri/src/manager.rs b/core/tauri/src/manager.rs
index b61982561..6d506788b 100644
--- a/core/tauri/src/manager.rs
+++ b/core/tauri/src/manager.rs
@@ -658,6 +658,11 @@ impl<P: Params> WindowManager<P> {
     mut pending: PendingWindow<P>,
     pending_labels: &[P::Label],
   ) -> crate::Result<PendingWindow<P>> {
+    if self.windows_lock().contains_key(&pending.label) {
+      return Err(crate::Error::WindowLabelAlreadyExists(
+        pending.label.to_string(),
+      ));
+    }
     let (is_local, url) = match &pending.webview_attributes.url {
       WindowUrl::App(path) => {
         let url = self.get_url();