diff --git a/libraries/AP_HAL_SITL/Util.cpp b/libraries/AP_HAL_SITL/Util.cpp
new file mode 100644
index 0000000000..00c34de66e
--- /dev/null
+++ b/libraries/AP_HAL_SITL/Util.cpp
@@ -0,0 +1,10 @@
+#include "Util.h"
+
+uint64_t HALSITL::Util::get_hw_rtc() const
+{
+    struct timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);
+    const uint64_t seconds = ts.tv_sec;
+    const uint64_t nanoseconds = ts.tv_nsec;
+    return (seconds * 1000000ULL + nanoseconds/1000ULL);
+}
diff --git a/libraries/AP_HAL_SITL/Util.h b/libraries/AP_HAL_SITL/Util.h
index 26821ebcef..9a7113eab1 100644
--- a/libraries/AP_HAL_SITL/Util.h
+++ b/libraries/AP_HAL_SITL/Util.h
@@ -28,6 +28,9 @@ public:
     const char* get_custom_defaults_file() const override {
         return sitlState->defaults_path;
     }
+
+    uint64_t get_hw_rtc() const override;
+
 private:
     SITL_State *sitlState;
 };