add missing id="ffi-prim"

diff --git a/docs/users_guide/ffi-chap.xml b/docs/users_guide/ffi-chap.xml
index 2d2c5a0..f9f52ae 100644 (file)
--- a/docs/users_guide/ffi-chap.xml
+++ b/docs/users_guide/ffi-chap.xml
@@ -64,7 +64,7 @@ OK:
 </para>
       </sect2>
 
-      <sect2>
+      <sect2 id="ffi-prim">
         <title>Primitive imports</title>
        <para>
          GHC extends the FFI with an additional calling convention