diff --git a/wagtail/admin/views/pages.py b/wagtail/admin/views/pages.py
index c30ca7fa3..8cf6edcf9 100644
--- a/wagtail/admin/views/pages.py
+++ b/wagtail/admin/views/pages.py
@@ -344,12 +344,21 @@ def edit(request, page_id):
     form_class = edit_handler.get_form_class()
 
     if page_perms.user_has_lock():
-        messages.warning(request, format_html(_("<b>Page '{}' was locked</b> by <b>you</b> on <b>{}</b>."), page.get_admin_display_title(), page.locked_at.strftime("%d %b %Y %H:%M")), extra_tags='lock')
-    if page_perms.page_locked():
-        locked_by_message = ""
-        if page.locked_by:
-            locked_by_message = format_html(" by <b>{}</b>", str(page.locked_by))
-        messages.error(request, format_html(_("<b>Page '{}' was locked</b>{} on <b>{}</b>."), page.get_admin_display_title(), locked_by_message, page.locked_at.strftime("%d %b %Y %H:%M")), extra_tags='lock')
+        if page.locked_at:
+            lock_message = format_html(_("<b>Page '{}' was locked</b> by <b>you</b> on <b>{}</b>."), page.get_admin_display_title(), page.locked_at.strftime("%d %b %Y %H:%M"))
+        else:
+            lock_message = format_html(_("<b>Page '{}' is locked</b> by <b>you</b>."), page.get_admin_display_title())
+
+        messages.warning(request, lock_message, extra_tags='lock')
+
+    elif page_perms.page_locked():
+        if page.locked_by and page.locked_at:
+            lock_message = format_html(_("<b>Page '{}' was locked</b> by <b>{}</b> on <b>{}</b>."), page.get_admin_display_title(), str(page.locked_by), page.locked_at.strftime("%d %b %Y %H:%M"))
+        else:
+            # Page was probably locked with an old version of Wagtail, or a script
+            lock_message = format_html(_("<b>Page '{}' is locked</b>."), page.get_admin_display_title())
+
+        messages.error(request, lock_message, extra_tags='lock')
 
     next_url = get_valid_next_url_from_request(request)