diff --git a/packages/unstyled/image-viewer/src/types.ts b/packages/unstyled/image-viewer/src/types.ts
index 725d491e6..1d01468c7 100644
--- a/packages/unstyled/image-viewer/src/types.ts
+++ b/packages/unstyled/image-viewer/src/types.ts
@@ -21,7 +21,7 @@ export interface InterfaceImageViewerProps {
   /**
    * If true, the ImageViewer will open. Useful for controllable state behavior.
    */
-  isOpen: boolean | undefined;
+  isOpen: boolean;
   /**
    * Callback invoked when the ImageViewer is closed.
    */