diff --git a/wp-includes/js/tinymce/tiny_mce_config.php b/wp-includes/js/tinymce/tiny_mce_config.php
index 215fa7e803..ef3c7c480d 100644
--- a/wp-includes/js/tinymce/tiny_mce_config.php
+++ b/wp-includes/js/tinymce/tiny_mce_config.php
@@ -49,11 +49,11 @@ function putFileContents( $path, $content ) {
 $https = ( isset($_SERVER['HTTPS']) && 'on' == strtolower($_SERVER['HTTPS']) ) ? true : false;
 	
 $baseurl = get_option('siteurl') . '/wp-includes/js/tinymce';
-if ( $https ) str_replace('http://', 'https://', $baseurl);
+if ( $https ) $baseurl = str_replace('http://', 'https://', $baseurl);
 
 $mce_css = $baseurl . '/wordpress.css';
 $mce_css = apply_filters('mce_css', $mce_css);
-if ( $https ) str_replace('http://', 'https://', $mce_css);
+if ( $https ) $mce_css = str_replace('http://', 'https://', $mce_css);
 
 $mce_locale = ( '' == get_locale() ) ? 'en' : strtolower( substr(get_locale(), 0, 2) ); // only ISO 639-1
 
@@ -104,7 +104,7 @@ if ( ! empty($mce_external_plugins) ) {
 
 	foreach ( $mce_external_plugins as $name => $url ) {
 		
-		if ( $https ) str_replace('http://', 'https://', $url);
+		if ( $https ) $url = str_replace('http://', 'https://', $url);
 		
 		$plugins[] = '-' . $name;
 
@@ -326,4 +326,4 @@ if ( '' != $cacheKey && is_dir($cache_path) && is_readable($cache_path) ) {
 	putFileContents( $cache_file, $content );
 }
 
-?>
\ No newline at end of file
+?>