diff --git a/src/core/ddsi/src/q_receive.c b/src/core/ddsi/src/q_receive.c
index 9e7f899..a442e86 100644
--- a/src/core/ddsi/src/q_receive.c
+++ b/src/core/ddsi/src/q_receive.c
@@ -1747,7 +1747,7 @@ static int handle_Gap (struct receiver_state *rst, nn_etime_t tnow, struct nn_rm
 
   if (!pwr->have_seen_heartbeat && pwr->n_reliable_readers > 0)
   {
-    DDS_TRACE(": no heartbeat seen yet", PGUID (pwr->e.guid), PGUID (dst));
+    DDS_TRACE(": no heartbeat seen yet");
     ddsrt_mutex_unlock (&pwr->e.lock);
     return 1;
   }
diff --git a/src/ddsrt/include/dds/ddsrt/log.h b/src/ddsrt/include/dds/ddsrt/log.h
index b6450c0..4a08a46 100644
--- a/src/ddsrt/include/dds/ddsrt/log.h
+++ b/src/ddsrt/include/dds/ddsrt/log.h
@@ -25,6 +25,7 @@
 #include <stdio.h>
 
 #include "dds/export.h"
+#include "dds/ddsrt/attributes.h"
 
 #if defined (__cplusplus)
 extern "C" {
@@ -199,7 +200,8 @@ dds_log(
     uint32_t line,
     const char *func,
     const char *fmt,
-    ...);
+    ...)
+  ddsrt_attribute_format((__printf__, 5, 6));
 
 /**
  * @brief Undecorated function name of the current function.
diff --git a/src/examples/roundtrip/pong.c b/src/examples/roundtrip/pong.c
index ef692f5..010c0c5 100644
--- a/src/examples/roundtrip/pong.c
+++ b/src/examples/roundtrip/pong.c
@@ -60,7 +60,7 @@ static void data_available(dds_entity_t rd, void *arg)
       RoundTripModule_DataType * valid_sample = &data[j];
       status = dds_write_ts (writer, valid_sample, info[j].source_timestamp);
       if (status < 0)
-        DDS_FATAL("dds_write_ts: %s\n", -status);
+        DDS_FATAL("dds_write_ts: %d\n", -status);
     }
   }
 }