diff --git a/src/libcharon/plugins/vici/vici_builder.c b/src/libcharon/plugins/vici/vici_builder.c
index 82f12c9da..129eb4d4c 100644
--- a/src/libcharon/plugins/vici/vici_builder.c
+++ b/src/libcharon/plugins/vici/vici_builder.c
@@ -145,6 +145,7 @@ static void vadd_kv_or_li(private_vici_builder_t *this, char *key,
 	{
 		value = chunk_alloc(len + 1);
 		len = vsnprintf(value.ptr, value.len, fmt, args);
+		value.len = len;
 	}
 	else
 	{