Index: src/wp-includes/post-template.php
===================================================================
--- src/wp-includes/post-template.php	(revision 28248)
+++ src/wp-includes/post-template.php	(working copy)
@@ -265,7 +265,8 @@
 		if ( $more ) {
 			$output .= '<span id="more-' . $post->ID . '"></span>' . $content[1];
 		} else {
-			if ( ! empty( $more_link_text ) )
+			if ( ! empty( $more_link_text ) ) {
+				$more_link_text = preg_replace( '/ (?![^<>]*>)/', '&nbsp;', $more_link_text );
 
 				/**
 				 * Filter the Read More link text.
@@ -276,6 +277,7 @@
 				 * @param string $more_link_text    Read More text.
 				 */
 				$output .= apply_filters( 'the_content_more_link', ' <a href="' . get_permalink() . "#more-{$post->ID}\" class=\"more-link\">$more_link_text</a>", $more_link_text );
+			}
 			$output = force_balance_tags( $output );
 		}
 	}