diff --git a/bin/isolated-functions.sh b/bin/isolated-functions.sh
index 6bd33cb..edeb93a 100755
--- a/bin/isolated-functions.sh
+++ b/bin/isolated-functions.sh
@@ -485,6 +485,9 @@
 			ROOT ROOTPATH RPMDIR STARTDIR TMP TMPDIR USE_EXPAND \
 			WARN XARGS _RC_GET_KV_CACHE
 
+		# user config variables
+		unset DOC_SYMLINKS_DIR INSTALL_MASK PKG_INSTALL_MASK
+
 		set
 		export
 	)
diff --git a/pym/portage/__init__.py b/pym/portage/__init__.py
index db580c4..c51497e 100644
--- a/pym/portage/__init__.py
+++ b/pym/portage/__init__.py
@@ -936,6 +936,11 @@
 		"XARGS",
 	]
 
+	# user config variables
+	_environ_whitelist += [
+		"DOC_SYMLINKS_DIR", "INSTALL_MASK", "PKG_INSTALL_MASK"
+	]
+
 	_environ_whitelist += [
 		"A", "AA", "CATEGORY", "P", "PF", "PN", "PR", "PV", "PVR"
 	]