diff --git a/c/src/libchip/rtc/mc146818a.h b/c/src/libchip/rtc/mc146818a.h
index 7ce3b60885..7f13261d34 100644
--- a/c/src/libchip/rtc/mc146818a.h
+++ b/c/src/libchip/rtc/mc146818a.h
@@ -48,6 +48,9 @@
  *  Driver function table
  */
 extern rtc_fns mc146818a_fns;
+boolean mc146818a_probe(
+  int minor
+);
 
 /*
  * Default register access routines