diff --git a/frontend_tests/node_tests/top_left_corner.js b/frontend_tests/node_tests/top_left_corner.js
index 07fcbc794a..d21c715870 100644
--- a/frontend_tests/node_tests/top_left_corner.js
+++ b/frontend_tests/node_tests/top_left_corner.js
@@ -29,8 +29,15 @@ run_test('narrowing', () => {
         user_id: 1,
         full_name: 'Alice Smith',
     };
-    people.add(alice);
+    const bob = {
+        email: 'bob@example.com',
+        user_id: 2,
+        full_name: 'Bob Patel',
+    };
+
     people.add_in_realm(alice);
+    people.add_in_realm(bob);
+
     pm_expanded = false;
     filter = new Filter([
         {operator: 'pm-with', operand: 'alice@example.com'},
@@ -38,6 +45,13 @@ run_test('narrowing', () => {
     top_left_corner.handle_narrow_activated(filter);
     assert(pm_expanded);
 
+    pm_expanded = false;
+    filter = new Filter([
+        {operator: 'pm-with', operand: 'bob@example.com,alice@example.com'},
+    ]);
+    top_left_corner.handle_narrow_activated(filter);
+    assert(pm_expanded);
+
     pm_expanded = false;
     filter = new Filter([
         {operator: 'pm-with', operand: 'not@valid.com'},
diff --git a/static/js/top_left_corner.js b/static/js/top_left_corner.js
index c785480e0d..5dddca8f7f 100644
--- a/static/js/top_left_corner.js
+++ b/static/js/top_left_corner.js
@@ -73,19 +73,35 @@ exports.handle_narrow_activated = function (filter) {
         }
     }
 
-    var op_is = filter.operands('is');
-    var op_pm = filter.operands('pm-with');
-    if (op_is.length >= 1 && _.contains(op_is, "private") || op_pm.length >= 1) {
-        if (!people.is_valid_bulk_emails_for_compose(op_pm)) {
-            // Don't go into the else statement and close the pm_list.
-            return;
-        }
+    if (exports.should_expand_pm_list(filter)) {
+        var op_pm = filter.operands('pm-with');
         pm_list.expand(op_pm);
     } else {
         pm_list.close();
     }
 };
 
+exports.should_expand_pm_list = function (filter) {
+    var op_is = filter.operands('is');
+
+    if (op_is.length >= 1 && _.contains(op_is, "private")) {
+        return true;
+    }
+
+    var op_pm = filter.operands('pm-with');
+
+    if (op_pm.length !== 1) {
+        return false;
+    }
+
+    var emails_strings = op_pm[0];
+    var emails = emails_strings.split(',');
+
+    var has_valid_emails = people.is_valid_bulk_emails_for_compose(emails);
+
+    return has_valid_emails;
+};
+
 exports.handle_narrow_deactivated = function () {
     deselect_top_left_corner_items();
     pm_list.close();