diff --git a/rpm_spec/core-vm.spec b/rpm_spec/core-vm.spec
index 686aadc..f8329f3 100644
--- a/rpm_spec/core-vm.spec
+++ b/rpm_spec/core-vm.spec
@@ -66,6 +66,7 @@ Obsoletes:  qubes-core-proxyvm
 Obsoletes:  qubes-upgrade-vm < 2.0
 BuildRequires: xen-devel
 BuildRequires: qubes-utils-devel >= 2.0.5
+BuildRequires: libX11-devel
 
 %define _builddir %(pwd)