diff --git a/docs/changelog/7.x.x.txt b/docs/changelog/7.x.x.txt
index b5cdbbe34..9f6a68e7d 100644
--- a/docs/changelog/7.x.x.txt
+++ b/docs/changelog/7.x.x.txt
@@ -13,6 +13,7 @@
  - fixed #11347: copy forum
  - fixed #11359: USPS International shipping does not work on United Kingdom
  - fixed #11034: Upgrade errors -- 7.6.35 to 7.7.17
+ - fixed #11346: Slow rendering of Thread asset with a lot of attachments
 
 7.8.9
  - fixed #11235: wiki search
diff --git a/lib/WebGUI/Storage.pm b/lib/WebGUI/Storage.pm
index 2bf5898a2..a75149a0b 100644
--- a/lib/WebGUI/Storage.pm
+++ b/lib/WebGUI/Storage.pm
@@ -1247,14 +1247,15 @@ sub getThumbnailUrl {
 	my $self = shift;
 	my $filename = shift;
 	if (! defined $filename) {
-		$self->session->errorHandler->error("Can't make a thumbnail url without a filename.");
+		$self->session->errorHandler->error("Can't find a thumbnail url without a filename.");
 		return '';
 	}
-    if (! isIn($filename, @{ $self->getFiles() })) {
-        $self->session->errorHandler->error("Can't make a thumbnail for a file named '$filename' that is not in my storage location.");
+    my $thumbname = 'thumb-' . $filename;
+    if (! -e $self->getPath($thumbname)) {
+        $self->session->errorHandler->error("Can't find a thumbnail for a file named '$filename' that is not in my storage location.");
         return '';
     }
-	return $self->getUrl("thumb-".$filename);
+	return $self->getUrl($thumbname);
 }
 
 #-------------------------------------------------------------------
diff --git a/t/Storage/Image.t b/t/Storage/Image.t
index fb6441638..4a04d5bcd 100644
--- a/t/Storage/Image.t
+++ b/t/Storage/Image.t
@@ -203,10 +203,10 @@ is($imageCopy->deleteFile('../../'), undef, 'deleteFile in Storage::Image also r
 ####################################################
 
 is($thumbStore->getThumbnailUrl(), '', 'getThumbnailUrl returns undef if no file is sent');
-is($WebGUI::Test::logger_error, q/Can't make a thumbnail url without a filename./, 'getThumbnailUrl logs an error message for not sending a filename');
+is($WebGUI::Test::logger_error, q/Can't find a thumbnail url without a filename./, 'getThumbnailUrl logs an error message for not sending a filename');
 
 is($thumbStore->getThumbnailUrl('round.png'), '', 'getThumbnailUrl returns undef if the requested file is not in the storage location');
-is($WebGUI::Test::logger_error, q/Can't make a thumbnail for a file named 'round.png' that is not in my storage location./, 'getThumbnailUrl logs an error message for not sending a filename');
+is($WebGUI::Test::logger_error, q/Can't find a thumbnail for a file named 'round.png' that is not in my storage location./, 'getThumbnailUrl logs an error message for not sending a filename');
 
 is($thumbStore->getThumbnailUrl('square.png'), $thumbStore->getUrl('thumb-square.png'), 'getThumbnailUrl returns the correct url');