diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -75,6 +75,9 @@
 CWARNFLAGS+=	-Wno-uninitialized
 .endif # WARNS >=2 && WARNS <= 4
 CWARNFLAGS+=	-Wno-pointer-sign
+.if !defined(NO_WDATE_TIME)
+CWARNFLAGS+=	-Wdate-time
+.endif # NO_WDATE_TIME
 # Clang has more warnings enabled by default, and when using -Wall, so if WARNS
 # is set to low values, these have to be disabled explicitly.
 .if ${WARNS} <= 6