diff --git a/src/merge/timestamp_calculator.cpp b/src/merge/timestamp_calculator.cpp
index 37776d02e..6b0d1fefd 100644
--- a/src/merge/timestamp_calculator.cpp
+++ b/src/merge/timestamp_calculator.cpp
@@ -45,10 +45,17 @@ timestamp_calculator_c::add_timestamp(timestamp_c const &timestamp,
 void
 timestamp_calculator_c::add_timestamp(int64_t timestamp,
                                       boost::optional<uint64_t> stream_position) {
-  if (-1 != timestamp)
+  if (0 <= timestamp)
     add_timestamp(timestamp_c::ns(timestamp), stream_position);
 }
 
+void
+timestamp_calculator_c::add_timestamp(boost::optional<int64_t> const &timestamp,
+                                      boost::optional<uint64_t> stream_position) {
+  if (timestamp && (0 <= *timestamp))
+    add_timestamp(timestamp_c::ns(*timestamp), stream_position);
+}
+
 void
 timestamp_calculator_c::add_timestamp(packet_cptr const &packet,
                                       boost::optional<uint64_t> stream_position) {
diff --git a/src/merge/timestamp_calculator.h b/src/merge/timestamp_calculator.h
index 6e06705fe..06e47410c 100644
--- a/src/merge/timestamp_calculator.h
+++ b/src/merge/timestamp_calculator.h
@@ -34,6 +34,7 @@ private:
 public:
   timestamp_calculator_c(int64_t samples_per_second);
 
+  void add_timestamp(boost::optional<int64_t> const &timestamp, boost::optional<uint64_t> stream_position = boost::none);
   void add_timestamp(timestamp_c const &timestamp, boost::optional<uint64_t> stream_position = boost::none);
   void add_timestamp(int64_t timestamp, boost::optional<uint64_t> stream_position = boost::none);
   void add_timestamp(packet_cptr const &packet, boost::optional<uint64_t> stream_position = boost::none);