diff --git a/scheme/cyclone/hashset.sld b/scheme/cyclone/hashset.sld
new file mode 100644
index 00000000..ccd35c06
--- /dev/null
+++ b/scheme/cyclone/hashset.sld
@@ -0,0 +1,67 @@
+
+;;;; Cyclone Scheme
+;;;; https://github.com/justinethier/cyclone
+;;;;
+;;;; Copyright (c) 2018, Justin Ethier
+;;;; All rights reserved.
+;;;;
+;;;; This module contains a hashset based on code from:
+;;;; https://github.com/avsej/hashset.c
+;;;;
+(define-library (scheme cyclone pretty-print)
+    (export
+    )
+    (import (scheme base)
+            (scheme write))
+    (include-c-header "cyclone/hashset.h")
+    (begin
+
+(define-c hs-create
+  "(void *data, int argc, closure _, object k )"
+  "
+    hashset_t hs = hashset_create();
+    make_c_opaque(opq, hs);
+    return_closcall1(data, k, &opq);
+  ")
+
+(define-c hs-destroy
+  "(void *data, int argc, closure _, object k, object opq )"
+  "
+    hashset_t hs = (hashset_t)(opaque_ptr(opq));
+    hashset_destroy(hs);
+    return_closcall1(data, k, boolean_t);
+  ")
+
+(define-c hs-num-items
+  "(void *data, int argc, closure _, object k, object opq )"
+  "
+    hashset_t hs = (hashset_t)(opaque_ptr(opq));
+    int count = hashset_num_items(hs);
+    return_closcall1(data, k, obj_int2obj(count));
+  ")
+
+(define-c hs-add
+  "(void *data, int argc, closure _, object k, object opq, object item )"
+  "
+    hashset_t hs = (hashset_t)(opaque_ptr(opq));
+    int rv = hashset_add(hs, item);
+    return_closcall1(data, k, obj_int2obj(rv));
+  ")
+
+(define-c hs-remove
+  "(void *data, int argc, closure _, object k, object opq, object item )"
+  "
+    hashset_t hs = (hashset_t)(opaque_ptr(opq));
+    int rv = hashset_remove(hs, item);
+    return_closcall1(data, k, obj_int2obj(rv));
+  ")
+
+(define-c hs-member?
+  "(void *data, int argc, closure _, object k, object opq, object item )"
+  "
+    hashset_t hs = (hashset_t)(opaque_ptr(opq));
+    int rv = hashset_is_member(hs, item);
+    return_closcall1(data, k, rv ? boolean_t : boolean_f);
+  ")
+
+))