diff --git a/rubygem-childprocess.spec b/rubygem-childprocess.spec
index e96b3a6..b3e17f6 100644
--- a/rubygem-childprocess.spec
+++ b/rubygem-childprocess.spec
@@ -15,6 +15,7 @@ BuildRequires: rubygems-devel
 BuildRequires: rubygem(ffi)
 BuildRequires: rubygem(rspec) >= 3
 BuildArch: noarch
+# posix_spaw is not implemented everywhere, use just Intel for build.
 ExclusiveArch: %{ix86} x86_64 noarch
 
 %description