diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index ea948939d5f4..89083ae1aebe 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -44,7 +44,7 @@ enum { ERRORS };
 
 static const char *err_text[] = { ERRORS };
 
-DEFINE_MUTEX(lastcmd_mutex);
+static DEFINE_MUTEX(lastcmd_mutex);
 static char *last_cmd;
 
 static int errpos(const char *str)