diff --git a/include/libbb.h b/include/libbb.h
index d74f802..7bc0dca 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -237,6 +237,7 @@
 #define errno (*bb_errno)
 #endif
 
+unsigned long long monotonic_ns(void) FAST_FUNC;
 unsigned long long monotonic_us(void) FAST_FUNC;
 unsigned monotonic_sec(void) FAST_FUNC;