diff --git a/wp-admin/includes/class-wp-filesystem-base.php b/wp-admin/includes/class-wp-filesystem-base.php
index 9d7d6e8c19..495d60139f 100644
--- a/wp-admin/includes/class-wp-filesystem-base.php
+++ b/wp-admin/includes/class-wp-filesystem-base.php
@@ -147,11 +147,39 @@ class WP_Filesystem_Base {
 	 */
 	function find_folder($folder) {
 
-		if ( strpos($this->method, 'ftp') !== false ) {
-			$constant_overrides = array( 'FTP_BASE' => ABSPATH, 'FTP_CONTENT_DIR' => WP_CONTENT_DIR, 'FTP_PLUGIN_DIR' => WP_PLUGIN_DIR, 'FTP_LANG_DIR' => WP_LANG_DIR );
-			foreach ( $constant_overrides as $constant => $dir )
-				if ( defined($constant) && $folder === $dir )
-					return trailingslashit(constant($constant));
+		if ( isset( $this->cache[ $folder ] ) )
+			return $this->cache[ $folder ];
+
+		if ( stripos($this->method, 'ftp') !== false ) {
+			$constant_overrides = array(
+				'FTP_BASE' => ABSPATH,
+				'FTP_CONTENT_DIR' => WP_CONTENT_DIR,
+				'FTP_PLUGIN_DIR' => WP_PLUGIN_DIR,
+				'FTP_LANG_DIR' => WP_LANG_DIR
+			);
+
+			// Direct matches ( folder = CONSTANT/ )
+			foreach ( $constant_overrides as $constant => $dir ) {
+				if ( ! defined( $constant ) )
+					continue;
+				if ( $folder === $dir )
+					return trailingslashit( constant( $constant ) );
+			}
+
+			// Prefix Matches ( folder = CONSTANT/subdir )
+			foreach ( $constant_overrides as $constant => $dir ) {
+				if ( ! defined( $constant ) )
+					continue;
+				if ( 0 === stripos( $folder, $dir ) ) { // $folder starts with $dir
+					$potential_folder = preg_replace( '#^' . preg_quote( $dir, '#' ) . '/#i', trailingslashit( constant( $constant ) ), $folder );
+					$potential_folder = trailingslashit( $potential_folder );
+
+					if ( $this->is_dir( $potential_folder ) ) {
+						$this->cache[ $folder ] = $potential_folder;
+						return $potential_folder;
+					}
+				}
+			}
 		} elseif ( 'direct' == $this->method ) {
 			$folder = str_replace('\\', '/', $folder); //Windows path sanitisation
 			return trailingslashit($folder);