diff --git a/web/src/pm_list.js b/web/src/pm_list.js
index 3b367c9bd8..2a0fcf78ab 100644
--- a/web/src/pm_list.js
+++ b/web/src/pm_list.js
@@ -31,7 +31,7 @@ export function set_count(count) {
     ui_util.update_unread_count_in_dom(get_private_messages_section_header(), count);
 }
 
-function close() {
+export function close() {
     private_messages_collapsed = true;
     $("#toggle_private_messages_section_icon").removeClass("fa-caret-down");
     $("#toggle_private_messages_section_icon").addClass("fa-caret-right");
@@ -100,7 +100,13 @@ export function update_private_messages() {
 }
 
 export function expand() {
+    // Only one thing can be zoomed at a time.
+    if (topic_zoom.is_zoomed_in()) {
+        topic_zoom.zoom_out();
+    }
+
     private_messages_collapsed = false;
+
     $("#toggle_private_messages_section_icon").addClass("fa-caret-down");
     $("#toggle_private_messages_section_icon").removeClass("fa-caret-right");
     update_private_messages();
diff --git a/web/src/topic_zoom.js b/web/src/topic_zoom.js
index f87d333265..7f46d0f642 100644
--- a/web/src/topic_zoom.js
+++ b/web/src/topic_zoom.js
@@ -1,5 +1,6 @@
 import $ from "jquery";
 
+import * as pm_list from "./pm_list";
 import * as popovers from "./popovers";
 import * as stream_list from "./stream_list";
 import * as topic_list from "./topic_list";
@@ -15,6 +16,7 @@ function zoom_in() {
     const stream_id = topic_list.active_stream_id();
 
     popovers.hide_all_except_sidebars();
+    pm_list.close();
     topic_list.zoom_in();
     stream_list.zoom_in_topics({
         stream_id,