diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 9f748f10..f9c18419 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -93,6 +93,16 @@ object Cyc_global_set(void *thd, object *glo, object value);
   } \
   return_closcall1(data, cont, &d)
 
+#define return_exact_double_op(data, cont, OP, z) \
+  make_int(i, 0); \
+  Cyc_check_num(data, z); \
+  if (type_of(z) == integer_tag) { \
+    i.value = (int)OP(((integer_type *)z)->value); \
+  } else { \
+    i.value = (int)OP(((double_type *)z)->value); \
+  } \
+  return_closcall1(data, cont, &i)
+
 /* Prototypes for primitive functions. */
 
 extern object Cyc_global_variables;
diff --git a/scheme/base.sld b/scheme/base.sld
index aaa00a65..71adc40b 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -92,6 +92,10 @@
     cond-expand
     when
     quasiquote
+    floor
+    ceiling
+    truncate
+    round
   )
   (begin
     ;; Features implemented by this Scheme
@@ -648,4 +652,16 @@
           (else 
              #f))))
 
+  (define-c floor
+    "(void *data, int argc, closure _, object k, object z)"
+    " return_exact_double_op(data, k, floor, z); ")
+  (define-c ceiling
+    "(void *data, int argc, closure _, object k, object z)"
+    " return_exact_double_op(data, k, ceil, z); ")
+  (define-c truncate
+    "(void *data, int argc, closure _, object k, object z)"
+    " return_exact_double_op(data, k, (int), z); ")
+  (define-c round
+    "(void *data, int argc, closure _, object k, object z)"
+    " return_exact_double_op(data, k, round, z); ")
 ))