diff --git a/wp-admin/includes/image.php b/wp-admin/includes/image.php
index a764432a18..2e79578e23 100644
--- a/wp-admin/includes/image.php
+++ b/wp-admin/includes/image.php
@@ -301,7 +301,11 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 			// The image may need to be converted regardless of its dimensions.
 			$output_format = wp_get_image_editor_output_format( $file, $imagesize['mime'] );
 
-			if ( is_array( $output_format ) && array_key_exists( $imagesize['mime'], $output_format ) ) {
+			if (
+				is_array( $output_format ) &&
+				array_key_exists( $imagesize['mime'], $output_format ) &&
+				$output_format[ $imagesize['mime'] ] !== $imagesize['mime']
+			) {
 				$convert = true;
 			}
 		}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 9a6bda7377..645b8cf381 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.8-alpha-59364';
+$wp_version = '6.8-alpha-59366';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.