diff --git a/configure.ac b/configure.ac
index f8fc6792b..d738fc4c6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,7 +14,7 @@ AM_SILENT_RULES
 AC_CONFIG_HEADERS(config.h)
 AC_CONFIG_MACRO_DIR([m4])
 
-AC_DEFINE(PROTOCOL_VERSION, "0.20.0", [The MPD protocol version])
+AC_DEFINE(PROTOCOL_VERSION, "0.21.0", [The MPD protocol version])
 
 GIT_COMMIT=`GIT_DIR="$srcdir/.git" git describe --dirty --always 2>/dev/null`
 if test x$GIT_COMMIT != x; then