diff --git a/wp-admin/includes/image.php b/wp-admin/includes/image.php
index 157169ce6e..a764432a18 100644
--- a/wp-admin/includes/image.php
+++ b/wp-admin/includes/image.php
@@ -291,7 +291,22 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 		 * If the original image's dimensions are over the threshold,
 		 * scale the image and use it as the "full" size.
 		 */
+		$scale_down = false;
+		$convert    = false;
+
 		if ( $threshold && ( $image_meta['width'] > $threshold || $image_meta['height'] > $threshold ) ) {
+			// The image will be converted if needed on saving.
+			$scale_down = true;
+		} else {
+			// 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 ) ) {
+				$convert = true;
+			}
+		}
+
+		if ( $scale_down || $convert ) {
 			$editor = wp_get_image_editor( $file );
 
 			if ( is_wp_error( $editor ) ) {
@@ -299,14 +314,20 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 				return $image_meta;
 			}
 
-			// Resize the image.
-			$resized = $editor->resize( $threshold, $threshold );
+			if ( $scale_down ) {
+				// Resize the image. This will also convet it if needed.
+				$resized = $editor->resize( $threshold, $threshold );
+			} elseif ( $convert ) {
+				// The image will be converted (if possible) when saved.
+				$resized = true;
+			}
+
 			$rotated = null;
 
 			// If there is EXIF data, rotate according to EXIF Orientation.
 			if ( ! is_wp_error( $resized ) && is_array( $exif_meta ) ) {
 				$resized = $editor->maybe_exif_rotate();
-				$rotated = $resized;
+				$rotated = $resized; // bool true or WP_Error
 			}
 
 			if ( ! is_wp_error( $resized ) ) {
@@ -314,7 +335,11 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 				 * Append "-scaled" to the image file name. It will look like "my_image-scaled.jpg".
 				 * This doesn't affect the sub-sizes names as they are generated from the original image (for best quality).
 				 */
-				$saved = $editor->save( $editor->generate_filename( 'scaled' ) );
+				if ( $scale_down ) {
+					$saved = $editor->save( $editor->generate_filename( 'scaled' ) );
+				} else {
+					$saved = $editor->save();
+				}
 
 				if ( ! is_wp_error( $saved ) ) {
 					$image_meta = _wp_image_meta_replace_original( $saved, $file, $image_meta, $attachment_id );
diff --git a/wp-includes/media.php b/wp-includes/media.php
index 8d1125ceca..b47730e28a 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -6233,16 +6233,23 @@ function wp_high_priority_element_flag( $value = null ) {
  * @return string[] An array of mime type mappings.
  */
 function wp_get_image_editor_output_format( $filename, $mime_type ) {
+	$default_output_format = array(
+		'image/heic'          => 'image/jpeg',
+		'image/heif'          => 'image/jpeg',
+		'image/heic-sequence' => 'image/jpeg',
+		'image/heif-sequence' => 'image/jpeg',
+	);
+
 	/**
 	 * Filters the image editor output format mapping.
 	 *
-	 * Enables filtering the mime type used to save images. By default,
-	 * the mapping array is empty, so the mime type matches the source image.
+	 * Enables filtering the mime type used to save images. By default HEIC/HEIF images
+	 * are converted to JPEGs.
 	 *
 	 * @see WP_Image_Editor::get_output_format()
 	 *
 	 * @since 5.8.0
-	 * @since 6.7.0 The default was changed from array() to array( 'image/heic' => 'image/jpeg' ).
+	 * @since 6.7.0 The default was changed from empty array to array containing the HEIC mime types.
 	 *
 	 * @param string[] $output_format {
 	 *     An array of mime type mappings. Maps a source mime type to a new
@@ -6253,5 +6260,5 @@ function wp_get_image_editor_output_format( $filename, $mime_type ) {
 	 * @param string $filename  Path to the image.
 	 * @param string $mime_type The source image mime type.
 	 */
-	return apply_filters( 'image_editor_output_format', array( 'image/heic' => 'image/jpeg' ), $filename, $mime_type );
+	return apply_filters( 'image_editor_output_format', $default_output_format, $filename, $mime_type );
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b6c825543a..6bf925d444 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.8-alpha-59316';
+$wp_version = '6.8-alpha-59317';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.