diff --git a/libguile/pairs.c b/libguile/pairs.c
index cf2782a06..03610f292 100644
--- a/libguile/pairs.c
+++ b/libguile/pairs.c
@@ -101,7 +101,7 @@ scm_cdr (SCM pair)
 }
 
 SCM
-scm_i_chase_pairs (SCM tree, scm_t_bits pattern)
+scm_i_chase_pairs (SCM tree, scm_t_uint32 pattern)
 {
   do
     {