diff --git a/Makefile b/Makefile
index de25876669..302582d6b5 100644
--- a/Makefile
+++ b/Makefile
@@ -428,6 +428,7 @@ unexport QMAKESPEC
 unexport RANLIB
 unexport TAR_OPTIONS
 unexport TERMINFO
+unexport TOPDIR
 
 GNU_HOST_NAME := $(shell support/gnuconfig/config.guess)