diff --git a/toys/README b/toys/README
index df08137..e518275 100644
--- a/toys/README
+++ b/toys/README
@@ -1,3 +1,8 @@
 checkextensions
 ===============
 Reports files whose extension does not match the (detected) mime-type.
+
+Options:
+	-u:	update source directory
+	-r:	rename files
+	-n:	(with -r): show what would be done.
diff --git a/toys/checkextensions b/toys/checkextensions
index 5ee9167..585d48c 100755
--- a/toys/checkextensions
+++ b/toys/checkextensions
@@ -41,11 +41,20 @@ do
 	source "$function"
 done
 
+while getopts 'urn' opt
+do
+	case $opt in
+		u)	update=1	;;
+		r)	rename=1	;;
+		n)	pretend=1	;;
+	esac
+done
+
 getConfig
 
 openDatabase
 
-getFiles
+(( update )) && getFiles
 
 echo '
 	SELECT
@@ -59,6 +68,14 @@ echo '
 	;
 	SELECT	"AtOM:NoMoreFiles";
 ' >&3
+renameFile() {
+	echo $'\t'"${filename%.*}$extension"
+	if ! (( pretend ))
+	then
+		mv "$sourcepath/$filename" "$sourcepath/${filename%.*}$extension"
+		Update source_files filename "${filename%.*}$extension"
+	fi
+}
 
 while read -u4 line
 do
@@ -76,25 +93,33 @@ do
 		'audio/mpeg')
 			if [[ ${filename##*.} != mp3 ]]
 			then
-				echo "$filename: MP3 (.mp3)"
+				extension=.mp3
+				echo "$filename: MP3 ($extension)"
+				(( rename )) && renameFile
 			fi
 		;;
 		'application/ogg vorbis')
 			if [[ ${filename##*.} != ogg ]]
 			then
-				echo "$filename: Ogg Vorbis (.ogg)"
+				extension=.ogg
+				echo "$filename: Ogg Vorbis ($extension)"
+				(( rename )) && renameFile
 			fi
 		;;
 		'application/ogg opus')
 			if [[ ${filename##*.} != opus ]]
 			then
-				echo "$filename: Opus (.opus)"
+				extension=.opus
+				echo "$filename: Opus ($extension)"
+				(( rename )) && renameFile
 			fi
 		;;
 		'audio/x-flac')
 			if [[ ${filename##*.} != flac ]]
 			then
-				echo "$filename: FLAC (.flac)"
+				extension=.flac
+				echo "$filename: FLAC ($extension)"
+				(( rename )) && renameFile
 			fi
 		;;
 	esac