diff --git a/libraries/AP_RTC/AP_RTC.cpp b/libraries/AP_RTC/AP_RTC.cpp
index 0aba1356ca..654120dd6c 100644
--- a/libraries/AP_RTC/AP_RTC.cpp
+++ b/libraries/AP_RTC/AP_RTC.cpp
@@ -6,13 +6,6 @@
 
 extern const AP_HAL::HAL& hal;
 
-const char *AP_RTC::_clock_source_types[] = {
-    "GPS",
-    "SYSTEM_TIME",
-    "HW",
-    "NONE",
-};
-
 AP_RTC::AP_RTC()
 {
     AP_Param::setup_object_defaults(this, var_info);
diff --git a/libraries/AP_RTC/AP_RTC.h b/libraries/AP_RTC/AP_RTC.h
index 15c2aa7039..95ffddd2ff 100644
--- a/libraries/AP_RTC/AP_RTC.h
+++ b/libraries/AP_RTC/AP_RTC.h
@@ -46,8 +46,6 @@ public:
         return _singleton;
     }
 
-    static const char *_clock_source_types[];
-
 private:
 
     static AP_RTC *_singleton;