diff --git a/rpm_spec/core-vm.spec b/rpm_spec/core-vm.spec
index 995ec4e..77168c2 100644
--- a/rpm_spec/core-vm.spec
+++ b/rpm_spec/core-vm.spec
@@ -67,6 +67,7 @@ Obsoletes:  qubes-core-netvm
 Obsoletes:  qubes-core-proxyvm
 Obsoletes:  qubes-upgrade-vm < 2.0
 BuildRequires: xen-devel
+BuildRequires: libX11-devel
 BuildRequires: qubes-utils-devel >= 3.0.1
 BuildRequires: qubes-libvchan-%{backend_vmm}-devel