diff --git a/meta-poky/conf/local.conf.sample b/meta-poky/conf/local.conf.sample
index 365b6eb20c..304ee012ce 100644
--- a/meta-poky/conf/local.conf.sample
+++ b/meta-poky/conf/local.conf.sample
@@ -191,7 +191,7 @@ PATCHRESOLVE = "noop"
 # files and damages the build in ways which may not be easily recoverable.
 # It's necesary to monitor /tmp, if there is no space left the build will fail
 # with very exotic errors.
-BB_DISKMON_DIRS = "\
+BB_DISKMON_DIRS ??= "\
     STOPTASKS,${TMPDIR},1G,100K \
     STOPTASKS,${DL_DIR},1G,100K \
     STOPTASKS,${SSTATE_DIR},1G,100K \