diff --git a/test-immut.scm b/test-immut.scm
new file mode 100644
index 00000000..bbcbaa45
--- /dev/null
+++ b/test-immut.scm
@@ -0,0 +1,40 @@
+;; A temporary test file
+(import (scheme base) (scheme write))
+
+
+   (define-c immutable?
+     "(void *data, int argc, closure _, object k, object obj)"
+     "object result = boolean_f;
+      if (is_object_type(obj) &&
+          (type_of(obj) == pair_tag ||
+           type_of(obj) == vector_tag ||
+           type_of(obj) == bytevector_tag ||
+           type_of(obj) == string_tag
+          ) &&
+          immutable(obj) ) {
+        result = boolean_t;
+      }
+      return_closcall1(data, k, result); ")
+
+(define-c _Cyc-set-immutable!
+   "(void *data, int argc, closure _, object k, object obj, object val)"
+   "object result = boolean_f;
+    if (is_object_type(obj)) {
+      immutable(obj) = (val == boolean_f) ? 0 : 1;
+      result = boolean_t;
+    }
+    return_closcall1(data, k, result); ")
+
+(define lis '(1 2 3))
+
+(write
+  (list
+    (immutable? lis)
+    (immutable? (car lis))
+    (_Cyc-set-immutable! lis #f)
+    (immutable? lis)
+    (immutable? (car lis))
+    (set-car! lis 'a)
+    lis
+  )
+)