diff --git a/README.org b/README.org
index a1b357b5..cbec8b46 100644
--- a/README.org
+++ b/README.org
@@ -312,7 +312,8 @@ Ement.el doesn't support encrypted rooms natively, but it can be used transparen
 + Option ~ement-room-coalesce-events~ may now be set to (and defaults to) a maximum number of events to coalesce together.  (This avoids potential performance problems in rare cases.  See [[https://github.com/alphapapa/ement.el/issues/247][#247]].  Thanks to [[https://github.com/viiru-][Arto Jantunen]] for reporting and [[https://github.com/sergiodj][Sergio Durigan Junior]] for testing.)
 
 *Fixes*
-+ Replies to edited messages are correctly sent to the original event (whereas previously they were sent to the edit, which caused reactions to not be shown).  ([[https://github.com/alphapapa/ement.el/issues/230][#230]], [[https://github.com/alphapapa/ement.el/issues/277][#277]].  Thanks to [[https://github.com/phil-s][Phil Sainty]] for suggesting, and to [[https://github.com/dionisos2][dionisos]] for reporting.) 
++ Replies to edited messages are correctly sent to the original event (whereas previously they were sent to the edit, which caused reactions to not be shown).  ([[https://github.com/alphapapa/ement.el/issues/230][#230]], [[https://github.com/alphapapa/ement.el/issues/277][#277]].  Thanks to [[https://github.com/phil-s][Phil Sainty]] for suggesting, and to [[https://github.com/dionisos2][dionisos]] for reporting.)
++ Set ~filter-buffer-substring-function~ in room buffers to prevent undesired text properties from being included in copied text.  ([[https://github.com/alphapapa/ement.el/pull/278][#278]].  Thanks to [[https://github.com/phil-s][Phil Sainty]].)
 
 ** 0.15.1
 
diff --git a/ement-room.el b/ement-room.el
index 9492c54e..12614fad 100644
--- a/ement-room.el
+++ b/ement-room.el
@@ -2610,6 +2610,8 @@ and erases the buffer.
         imenu-create-index-function #'ement-room--imenu-create-index-function
         ;; TODO: Use EWOC header/footer for, e.g. typing messages.
         ement-ewoc (ewoc-create #'ement-room--pp-thing))
+  ;; Prevent line/wrap-prefix formatting properties being included in copied text.
+  (setq-local filter-buffer-substring-function #'ement-room--buffer-substring-filter)
   ;; Set the URL handler.  Note that `browse-url-handlers' was added in 28.1;
   ;; prior to that `browse-url-browser-function' served double-duty.
   ;; TODO: Remove compat code when requiring Emacs >=28.
@@ -2801,6 +2803,18 @@ data slot."
 Needed to display things in the header line."
   (replace-regexp-in-string (rx "%") "%%" string t t))
 
+(defun ement-room--buffer-substring-filter (beg end &optional delete)
+  "Value for `filter-buffer-substring-function' in Ement rooms.
+
+Strips the `line-prefix' and `wrap-prefix' text properties which
+are used when formatting certain Matrix events, but which should
+not be copied into other buffers."
+  (let ((string (funcall (default-value 'filter-buffer-substring-function)
+                         beg end delete)))
+    (remove-list-of-text-properties
+     0 (length string) '(line-prefix wrap-prefix) string)
+    string))
+
 ;;;;; Imenu
 
 (defconst ement-room-timestamp-header-imenu-format "%Y-%m-%d (%A) %H:%M"