diff --git a/Makefile.inc1 b/Makefile.inc1
index 773aea0796cf..bba32772cc97 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -813,16 +813,6 @@ _worldtmp: .PHONY
 	    ${OBJTREE}${.CURDIR}/world32/${.CURDIR}/lib/libc/.depend.${f}.*
 .endif
 .endfor
-# 20170724 remove stale lib/clang/libllvm/Options.inc file, of which there are
-# two different versions after r308421, one for llvm-lib, one for llvm-dlltool
-.for d in ${OBJTREE} ${WORLDTMP}
-.for f in ${d}${.CURDIR}/lib/clang/libllvm/Options.inc
-.if exists(${f}) || exists(${f}.d)
-	@echo Removing stale generated ${f} files
-	@rm -f ${f} ${f}.d
-.endif
-.endfor
-.endfor
 .for _dir in \
     lib lib/casper usr legacy/bin legacy/usr
 	mkdir -p ${WORLDTMP}/${_dir}
diff --git a/lib/clang/libllvm/Makefile b/lib/clang/libllvm/Makefile
index e02af194ac60..357758d90237 100644
--- a/lib/clang/libllvm/Makefile
+++ b/lib/clang/libllvm/Makefile
@@ -1302,6 +1302,16 @@ llvm-dlltool/Options.inc: ${LLVM_SRCS}/lib/ToolDrivers/llvm-dlltool/Options.td
 TGHDRS+=	llvm-dlltool/Options.inc
 CFLAGS.DlltoolDriver.cpp+=	-I${.OBJDIR}/llvm-dlltool
 
+beforebuild:
+# 20170724 remove stale Options.inc file, of which there are two different
+# versions after r308421, one for llvm-lib, one for llvm-dlltool
+.for f in Options.inc
+.if exists(${f}) || exists(${f}.d)
+	@echo Removing stale generated ${f} files
+	@rm -f ${f} ${f}.d
+.endif
+.endfor
+
 # Note: some rules are superfluous, not every combination is valid.
 .for arch in \
 	AArch64/AArch64 ARM/ARM Mips/Mips PowerPC/PPC Sparc/Sparc X86/X86