diff --git a/NEWS b/NEWS
index 5c40e4f6c..670cb3256 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,6 @@
 ver 0.20.19 (not yet released)
+* protocol
+  - validate absolute seek time, reject negative values
 * macOS: fix crash bug
 
 ver 0.20.18 (2018/02/24)
diff --git a/src/protocol/ArgParser.cxx b/src/protocol/ArgParser.cxx
index 47fdfa405..bdc28bcbf 100644
--- a/src/protocol/ArgParser.cxx
+++ b/src/protocol/ArgParser.cxx
@@ -164,6 +164,10 @@ SongTime
 ParseCommandArgSongTime(const char *s)
 {
 	auto value = ParseCommandArgFloat(s);
+	if (value < 0)
+		throw FormatProtocolError(ACK_ERROR_ARG,
+					  "Negative value not allowed: %s", s);
+
 	return SongTime::FromS(value);
 }