diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 690cb0b2..52c90ef7 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -440,9 +440,8 @@ int equal(object, object);
 object equalp(object, object);
 object Cyc_has_cycle(object lst);
 object Cyc_is_boolean(object o);
-//object Cyc_is_pair(object o);
 #define Cyc_is_pair(o) ((is_object_type(o) && ((list) o)->tag == pair_tag) ? boolean_t : boolean_f)
-object Cyc_is_null(object o);
+#define Cyc_is_null(o) make_boolean(o == NULL)
 object Cyc_is_number(object o);
 object Cyc_is_complex(object o);
 object Cyc_is_real(object o);
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 8a36c383..1d5fdcdf 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -626,6 +626,8 @@ typedef boolean_type *boolean;
 
 #define boolean_desc(x) (((boolean_type *) x)->desc)
 
+#define make_boolean(x) (x ? boolean_t : boolean_f)
+
 /**
  * @brief Symbols are similar to strings, but only one instance of each
  * unique symbol is created, so comparisons are O(1).
diff --git a/runtime.c b/runtime.c
index 791934f9..58b9e32b 100644
--- a/runtime.c
+++ b/runtime.c
@@ -1557,13 +1557,13 @@ object Cyc_is_boolean(object o)
 //    return boolean_t;
 //  return boolean_f;
 //}
-
-object Cyc_is_null(object o)
-{
-  if (o == NULL)
-    return boolean_t;
-  return boolean_f;
-}
+//
+//object Cyc_is_null(object o)
+//{
+//  if (o == NULL)
+//    return boolean_t;
+//  return boolean_f;
+//}
 
 object Cyc_is_number(object o)
 {