diff --git a/src/ui/webview/appkit/webview_appkit.mm b/src/ui/webview/appkit/webview_appkit.mm
index ea53406..e61d179 100644
--- a/src/ui/webview/appkit/webview_appkit.mm
+++ b/src/ui/webview/appkit/webview_appkit.mm
@@ -19,14 +19,16 @@
   ~Internal() { [webView_ release]; }
 
   auto load_url(const std::string &url) -> void {
-    NSString *urlString = [NSString stringWithUTF8String:url.c_str()];
-    NSURL *nsUrl = [NSURL URLWithString:urlString];
-    if (nsUrl) {
-      NSURLRequest *request = [NSURLRequest requestWithURL:nsUrl];
-      [webView_ loadRequest:request];
-    } else {
-      NSLog(@"Invalid URL string: %@", urlString);
+    NSString *url_ns_str = [NSString stringWithUTF8String:url.c_str()];
+    NSURL *url_ns = [NSURL URLWithString:url_ns_str];
+
+    if (!url_ns) {
+      NSLog(@"Invalid URL string: %@", url_ns_str);
+      return;
     }
+
+    NSURLRequest *request = [NSURLRequest requestWithURL:url_ns];
+    [webView_ loadRequest:request];
   }
 
   auto load_html(const std::string &html_path) -> void {
@@ -37,11 +39,21 @@ auto load_html(const std::string &html_path) -> void {
     NSURL *html_url = [bundle URLForResource:html_filename_without_extension
                                withExtension:@"html"];
 
-    [this->get_webview() loadFileURL:html_url
-             allowingReadAccessToURL:[html_url URLByDeletingLastPathComponent]];
+    if (!html_url) {
+      NSLog(@"Failed to load HTML file: %@", html_filename);
+      return;
+    }
+
+    [this->webView_ loadFileURL:html_url
+        allowingReadAccessToURL:[html_url URLByDeletingLastPathComponent]];
   }
 
-  auto get_webview() -> WKWebView * { return webView_; }
+  auto attach_to(NSWindow *window) -> void {
+    NSView *contentView = [window contentView];
+    [webView_ setFrame:contentView.bounds];
+    [webView_ setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+    [contentView addSubview:webView_];
+  }
 
 private:
   WKWebView *webView_;
@@ -51,25 +63,23 @@ auto load_html(const std::string &html_path) -> void {
 
 WebView::~WebView() { delete internal_; }
 
-auto WebView::resize() -> void {
-  // Implement resize if needed
-}
-
 auto WebView::attach_to(sourcemeta::native::Window &window) -> void {
   NSWindow *native_window = static_cast<NSWindow *>(window.handle());
-  WKWebView *webview = internal_->get_webview();
-
-  NSView *contentView = [native_window contentView];
-  [webview setFrame:contentView.bounds];
-  [webview setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
-  [contentView addSubview:webview];
+  assert(native_window);
+  internal_->attach_to(native_window);
 }
 
 auto WebView::load_url(const std::string &url) -> void {
+  if (url.empty()) {
+    return;
+  }
   internal_->load_url(url);
 }
 
 auto WebView::load_html(const std::string &html_path) -> void {
+  if (html_path.empty() || !html_path.ends_with(".html")) {
+    return;
+  }
   internal_->load_html(html_path);
 }
 } // namespace sourcemeta::native