diff --git a/qpid-proton.spec b/qpid-proton.spec
index 64b6152..34dc34f 100644
--- a/qpid-proton.spec
+++ b/qpid-proton.spec
@@ -1,4 +1,5 @@
 %global proton_datadir %{_datadir}/proton
+%global __cmake_in_source_build 1
 
 %global __provides_exclude_from ^%{proton_datadir}/examples/.*$
 %global __requires_exclude_from ^%{proton_datadir}/examples/.*$