diff --git a/Makefile b/Makefile
index 8b9c5d9141..90598844e2 100644
--- a/Makefile
+++ b/Makefile
@@ -329,6 +329,7 @@ unexport CONFIG_SITE
 unexport QMAKESPEC
 unexport TERMINFO
 unexport MACHINE
+unexport O
 
 GNU_HOST_NAME := $(shell support/gnuconfig/config.guess)