diff --git a/packages/block-library/src/post-comments-form/index.php b/packages/block-library/src/post-comments-form/index.php
index 652f5ce32ddc64..7ebbb7123fbc36 100644
--- a/packages/block-library/src/post-comments-form/index.php
+++ b/packages/block-library/src/post-comments-form/index.php
@@ -20,7 +20,7 @@ function render_block_core_post_comments_form( $attributes, $content, $block ) {
 
 	$classes = 'comment-respond'; // See comment further below.
 	if ( isset( $attributes['textAlign'] ) ) {
-		$classes .= 'has-text-align-' . $attributes['textAlign'];
+		$classes .= ' has-text-align-' . $attributes['textAlign'];
 	}
 
 	$wrapper_attributes = get_block_wrapper_attributes( array( 'class' => $classes ) );