diff --git a/sf-stream/include/ZmqPulseReceiver.hpp b/sf-stream/include/ZmqPulseReceiver.hpp
index f0c177b..1590283 100644
--- a/sf-stream/include/ZmqPulseReceiver.hpp
+++ b/sf-stream/include/ZmqPulseReceiver.hpp
@@ -22,7 +22,7 @@ public:
     ZmqPulseReceiver(const std::vector<std::string>& ipc_urls, void* ctx);
     ~ZmqPulseReceiver();
 
-    uint64_t get_next_pulse_id();
+    uint64_t get_next_pulse_id() const;
 };
 
 
diff --git a/sf-stream/src/ZmqPulseReceiver.cpp b/sf-stream/src/ZmqPulseReceiver.cpp
index 85abeab..ed94dd8 100644
--- a/sf-stream/src/ZmqPulseReceiver.cpp
+++ b/sf-stream/src/ZmqPulseReceiver.cpp
@@ -63,7 +63,7 @@ void* ZmqPulseReceiver::connect_socket(const string url)
     return socket;
 }
 
-uint64_t ZmqPulseReceiver::get_next_pulse_id()
+uint64_t ZmqPulseReceiver::get_next_pulse_id() const
 {
     uint64_t pulses[n_modules_];