diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 8fe19f8f..44d852bc 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -292,6 +292,7 @@ extern const object primitive_Cyc_91global_91vars;
 extern const object primitive_Cyc_91get_91cvar;
 extern const object primitive_Cyc_91set_91cvar_67;
 extern const object primitive_Cyc_91cvar_127;
+extern const object primitive_Cyc_91opaque_127;
 extern const object primitive_Cyc_91has_91cycle_127;
 extern const object primitive_Cyc_91spawn_91thread_67;
 extern const object primitive_Cyc_91end_91thread_67;
diff --git a/runtime.c b/runtime.c
index ae1916b6..fad67cf7 100644
--- a/runtime.c
+++ b/runtime.c
@@ -2709,6 +2709,12 @@ void _Cyc_91cvar_127(void *data, object cont, object args)
   return_closcall1(data, cont, Cyc_is_cvar(car(args)));
 }
 
+void _Cyc_91opaque_127(void *data, object cont, object args)
+{
+  Cyc_check_num_args(data, "Cyc-opaque?", 1, args);
+  return_closcall1(data, cont, Cyc_is_opaque(car(args)));
+}
+
 void _boolean_127(void *data, object cont, object args)
 {
   Cyc_check_num_args(data, "boolean?", 1, args);
@@ -3720,6 +3726,8 @@ static primitive_type Cyc_91set_91cvar_67_primitive =
     { {0}, primitive_tag, "Cyc-set-cvar!", &_Cyc_91set_91cvar_67 };
 static primitive_type Cyc_91cvar_127_primitive =
     { {0}, primitive_tag, "Cyc-cvar?", &_Cyc_91cvar_127 };
+static primitive_type Cyc_91opaque_127_primitive =
+    { {0}, primitive_tag, "Cyc-opaque?", &_Cyc_91opaque_127 };
 static primitive_type Cyc_91has_91cycle_127_primitive =
     { {0}, primitive_tag, "Cyc-has-cycle?", &_Cyc_91has_91cycle_127 };
 static primitive_type Cyc_91spawn_91thread_67_primitive =
@@ -3963,6 +3971,7 @@ const object primitive_Cyc_91global_91vars = &Cyc_91global_91vars_primitive;
 const object primitive_Cyc_91get_91cvar = &Cyc_91get_91cvar_primitive;
 const object primitive_Cyc_91set_91cvar_67 = &Cyc_91set_91cvar_67_primitive;
 const object primitive_Cyc_91cvar_127 = &Cyc_91cvar_127_primitive;
+const object primitive_Cyc_91opaque_127 = &Cyc_91opaque_127_primitive;
 const object primitive_Cyc_91has_91cycle_127 = &Cyc_91has_91cycle_127_primitive;
 const object primitive_Cyc_91spawn_91thread_67 =
     &Cyc_91spawn_91thread_67_primitive;
diff --git a/scheme/cyclone/cgen.sld b/scheme/cyclone/cgen.sld
index 6202bcc3..d1790828 100644
--- a/scheme/cyclone/cgen.sld
+++ b/scheme/cyclone/cgen.sld
@@ -512,7 +512,7 @@
      ((eq? p 'Cyc-get-cvar)          "Cyc_get_cvar")
      ((eq? p 'Cyc-set-cvar!)         "Cyc_set_cvar")
      ((eq? p 'Cyc-cvar?)             "Cyc_is_cvar")
-     ; TODO: ((eq? p 'Cyc-opaque?)           "Cyc_is_opaque")
+     ((eq? p 'Cyc-opaque?)           "Cyc_is_opaque")
      ((eq? p 'Cyc-has-cycle?)        "Cyc_has_cycle")
      ((eq? p 'Cyc-spawn-thread!)     "Cyc_spawn_thread")
      ((eq? p 'Cyc-end-thread!)       "Cyc_end_thread")
diff --git a/scheme/cyclone/transforms.sld b/scheme/cyclone/transforms.sld
index 71cbab1d..cd90dfa6 100644
--- a/scheme/cyclone/transforms.sld
+++ b/scheme/cyclone/transforms.sld
@@ -451,6 +451,7 @@
      Cyc-get-cvar
      Cyc-set-cvar!
      Cyc-cvar? ;; Cyclone-specific
+     Cyc-opaque?
      Cyc-has-cycle?
      Cyc-spawn-thread!
      Cyc-end-thread!
@@ -567,6 +568,7 @@
                   Cyc-get-cvar
                   Cyc-set-cvar!
                   Cyc-cvar?
+                  Cyc-opaque?
                   Cyc-spawn-thread!
                   Cyc-end-thread!
                   apply
diff --git a/scheme/eval.sld b/scheme/eval.sld
index 63ddce53..7ae08392 100644
--- a/scheme/eval.sld
+++ b/scheme/eval.sld
@@ -164,6 +164,7 @@
       (list 'Cyc-get-cvar Cyc-get-cvar)
       (list 'Cyc-set-cvar! Cyc-set-cvar!)
       (list 'Cyc-cvar? Cyc-cvar?)
+      (list 'Cyc-opaque? Cyc-opaque?)
       (list 'Cyc-has-cycle? Cyc-has-cycle?)
       (list 'Cyc-spawn-thread! Cyc-spawn-thread!)
       (list 'Cyc-end-thread! Cyc-end-thread!)