diff --git a/include/time.h b/include/time.h
index 5eb6f144a..d320fe3f1 100644
--- a/include/time.h
+++ b/include/time.h
@@ -134,6 +134,7 @@ extern struct _timezone {
 int __fastcall__ clock_getres (clockid_t clock_id, struct timespec *res);
 int __fastcall__ clock_gettime (clockid_t clock_id, struct timespec *tp);
 int __fastcall__ clock_settime (clockid_t clock_id, const struct timespec *tp);
+void tzset (void);
 
 #endif
 
diff --git a/libsrc/rp6502/tzset.c b/libsrc/rp6502/tzset.c
new file mode 100644
index 000000000..be4236f2f
--- /dev/null
+++ b/libsrc/rp6502/tzset.c
@@ -0,0 +1,9 @@
+#include <rp6502.h>
+#include <time.h>
+
+int clock_gettimezone (clockid_t clock_id, struct _timezone* tz);
+
+void tzset (void)
+{
+    clock_gettimezone (CLOCK_REALTIME, &_tz);
+}