diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47a6221b..b348e23f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,8 @@
   the browser; a failed `IO.close` is raised to the caller.
 
 ### Fixed
+- An out-of-process iframe, e.g. Chrome's PDF viewer for an embedded PDF, appearing while a web worker was connected
+  raised `'Page.enable' wasn't found` in the event thread. Only pages and iframes are now searched for its parent [#640]
 - A browser context whose `Target.disposeBrowserContext` timed out stayed registered, so every later `#reset` asked
   again and raised `Disposal of browser context ... is already pending` for the rest of the process. It's now
   forgotten either way, and `#reset` disposes the remaining contexts before raising the first error [#641]
diff --git a/lib/ferrum/contexts.rb b/lib/ferrum/contexts.rb
index f3b0a9d4..45cc7f73 100644
--- a/lib/ferrum/contexts.rb
+++ b/lib/ferrum/contexts.rb
@@ -178,8 +178,7 @@ def subscribe_target_created
         context_id = info["browserContextId"]
         add_context(context_id)
 
-        if info["type"] == "iframe" &&
-           (target = @contexts[context_id]&.find_target { |t| t.connected? && t.page.frame_by(id: info["targetId"]) })
+        if info["type"] == "iframe" && (target = find_frame_owner(context_id, info["targetId"]))
           @contexts[context_id]&.add_target(session_id: target.session_id, params: info)
         else
           @contexts[context_id]&.add_target(params: info)
@@ -205,6 +204,12 @@ def subscribe_target_created
       end
     end
 
+    def find_frame_owner(context_id, frame_id)
+      @contexts[context_id]&.find_target do |target|
+        (target.page? || target.iframe?) && target.connected? && target.page.frame_by(id: frame_id)
+      end
+    end
+
     def rearm_auto_attach(session_id, type)
       return unless RECURSIVE_AUTO_ATTACH_TYPES.include?(type)
 
diff --git a/sig/ferrum/contexts.rbs b/sig/ferrum/contexts.rbs
index 73c3ac76..c575b1a1 100644
--- a/sig/ferrum/contexts.rbs
+++ b/sig/ferrum/contexts.rbs
@@ -43,6 +43,8 @@ module Ferrum
 
     def subscribe_target_created: () -> void
 
+    def find_frame_owner: (String? context_id, String frame_id) -> Target?
+
     def rearm_auto_attach: (String session_id, String type) -> void
 
     def handle_attach: (Target? target, String session_id, Hash[String, untyped] params) -> void