diff --git a/Makefile.inc1 b/Makefile.inc1
index 3429d8312d3..81567af5897 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -94,6 +94,9 @@ X${COMPILER}?=	${${COMPILER}}
 # a cross compiler.
 .if ${XCC:N${CCACHE_BIN}:M/*}
 MK_CLANG_BOOTSTRAP=	no
+# Make sure sub-makes see the option as disabled so the hack in bsd.sys.mk to
+# work around incompatible headers in Clang's resource directory is enabled.
+.MAKEOVERRIDES+=	MK_CLANG_BOOTSTRAP
 .endif
 
 # Pull in compiler metadata from buildworld/toolchain if possible to avoid