diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 040c774b..4898870e 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -406,6 +406,7 @@ object Cyc_is_boolean(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);
 object Cyc_is_number(object o);
+object Cyc_is_complex(object o);
 object Cyc_is_real(object o);
 object Cyc_is_integer(object o);
 object Cyc_is_fixnum(object o);
diff --git a/runtime.c b/runtime.c
index 05337de2..b694aa55 100644
--- a/runtime.c
+++ b/runtime.c
@@ -1581,6 +1581,13 @@ object Cyc_is_real(object o)
   return Cyc_is_number(o);
 }
 
+object Cyc_is_complex(object o)
+{
+  if ((o != NULL) && !is_value_type(o) && ((list) o)->tag == complex_num_tag)
+    return boolean_t;
+  return boolean_f;
+}
+
 object Cyc_is_fixnum(object o)
 {
   if (obj_is_int(o))