diff --git a/C/unify.c b/C/unify.c
index 487a5e3fa..fb535df73 100644
--- a/C/unify.c
+++ b/C/unify.c
@@ -463,7 +463,7 @@ p_cyclic( USES_REGS1 )
   return rational_tree(t);
 }
 
-int Yap_IsAcyclicTerm(Term t)
+bool Yap_IsAcyclicTerm(Term t)
 {
   return !rational_tree(t);
 }