diff --git a/src/pyj/book_list/comments_editor.pyj b/src/pyj/book_list/comments_editor.pyj
index 9116e17051..eba17a4308 100644
--- a/src/pyj/book_list/comments_editor.pyj
+++ b/src/pyj/book_list/comments_editor.pyj
@@ -287,7 +287,7 @@ class CommentsEditorBoss:
             'exec_command': self.exec_command,
             'focus': self.focus,
         }
-        self.comm = IframeClient(handlers)
+        self.comm = IframeClient(handlers, 'comments-editor-iframe')
 
     def initialize(self, data):
         window.onerror = self.onerror
diff --git a/src/pyj/iframe_comm.pyj b/src/pyj/iframe_comm.pyj
index 280642058c..6f29279b0c 100644
--- a/src/pyj/iframe_comm.pyj
+++ b/src/pyj/iframe_comm.pyj
@@ -173,10 +173,14 @@ def create_wrapped_iframe(handlers, bootstrap_text, entry_point, kw):
     return iframe, ans
 
 
+client_instance_num = 0
+
 class IframeClient:
 
-    def __init__(self, handlers):
+    def __init__(self, handlers, name):
         self.encrypted_communications = False
+        self.name = name
+        self.instance_num = v'++client_instance_num'
         self.handlers = {k: handlers[k] for k in handlers}
         self.initialize_handler = handlers.initialize
         self.handlers.initialize = self.initialize
@@ -233,6 +237,7 @@ class IframeClient:
 
     def send_message(self, action, data):
         data.action = action
+        data.iframe_id = f'{self.name}-{self.instance_num}'
         if self.encrypted_communications:
             data = self.gcm_to_parent.encrypt(JSON.stringify(data))
         window.parent.postMessage(data, '*')
diff --git a/src/pyj/read_book/footnotes.pyj b/src/pyj/read_book/footnotes.pyj
index 7c14bad2b3..0938385176 100644
--- a/src/pyj/read_book/footnotes.pyj
+++ b/src/pyj/read_book/footnotes.pyj
@@ -191,7 +191,7 @@ class PopupIframeBoss:
             'clear': self.on_clear,
             'display': self.display,
         }
-        self.comm = IframeClient(handlers)
+        self.comm = IframeClient(handlers, 'popup-iframe')
         self.blob_url_map = {}
         self.name = None
         self.frag = None
diff --git a/src/pyj/read_book/iframe.pyj b/src/pyj/read_book/iframe.pyj
index 832bf082a8..4954aec0f1 100644
--- a/src/pyj/read_book/iframe.pyj
+++ b/src/pyj/read_book/iframe.pyj
@@ -169,7 +169,7 @@ class IframeBoss:
             'replace_highlights': self.replace_highlights,
             'clear_selection': def(): window.getSelection().removeAllRanges();,
         }
-        self.comm = IframeClient(handlers)
+        self.comm = IframeClient(handlers, 'main-iframe')
         self.last_window_ypos = 0
         self.length_before = None