diff --git a/profiles/base/package.use.mask b/profiles/base/package.use.mask
index 0bb2172a7ecd5..96832a07b0aff 100644
--- a/profiles/base/package.use.mask
+++ b/profiles/base/package.use.mask
@@ -7,6 +7,10 @@
 # This file is only for generic masks. For arch-specific masks (i.e.
 # mask everywhere, unmask on arch/*) use arch/base.
 
+# Michał Górny <mgorny@gentoo.org> (08 Dec 2018)
+# Requires z3-4.7.1+ that's not packaged in Gentoo.
+>=sys-devel/clang-8 z3
+
 # Michał Górny <mgorny@gentoo.org> (01 Dec 2018)
 # Moved from use.mask to specific packages.
 # Andreas Sturmlechner <asturm@gentoo.org> (10 May 2018)