diff --git a/src/array.c b/src/array.c
index 3dc1b94f3ecd6..9ed61a4ae144c 100644
--- a/src/array.c
+++ b/src/array.c
@@ -243,7 +243,7 @@ JL_DLLEXPORT jl_array_t *jl_reshape_array(jl_value_t *atype, jl_array_t *data,
     // introspect the object to update the a->data field. To avoid doing that and
     // making scan_object much more complex we simply enforce that both owner and
     // buffers are always pinned
-    mmtk_pin_object(owner);
+    PTR_PIN(owner);
     a->flags.how = 3;
     a->data = data->data;
     a->flags.isshared = 1;
@@ -296,7 +296,7 @@ JL_DLLEXPORT jl_array_t *jl_string_to_array(jl_value_t *str)
     // introspect the object to update the a->data field. To avoid doing that and
     // making scan_object much more complex we simply enforce that both owner and
     // buffers are always pinned
-    mmtk_pin_object(str);
+    PTR_PIN(str);
     a->flags.how = 3;
     a->flags.isshared = 1;
     size_t l = jl_string_len(str);
@@ -695,7 +695,7 @@ static int NOINLINE array_resize_buffer(jl_array_t *a, size_t newlen)
         // introspect the object to update the a->data field. To avoid doing that and
         // making scan_object much more complex we simply enforce that both owner and
         // buffers are always pinned
-        mmtk_pin_object(s);
+        PTR_PIN(s);
         jl_array_data_owner(a) = s;
         jl_gc_wb(a, s);
         a->data = jl_string_data(s);
diff --git a/src/builtins.c b/src/builtins.c
index 2ab4b7b8a18ad..157ad0257a95d 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -314,7 +314,7 @@ static uintptr_t type_object_id_(jl_value_t *v, jl_varidx_t *env) JL_NOTSAFEPOIN
         }
         // FIXME: Pinning objects that get hashed
         // until we implement address space hashing.
-        mmtk_pin_object(v);
+        PTR_PIN(v);
         return inthash((uintptr_t)v);
     }
     if (tv == jl_uniontype_type) {
@@ -364,7 +364,7 @@ static uintptr_t immut_id_(jl_datatype_t *dt, jl_value_t *v, uintptr_t h) JL_NOT
 
         // FIXME: Pinning objects that get hashed
         // until we implement address space hashing.
-        mmtk_pin_object(v);
+        PTR_PIN(v);
         // operate element-wise if there are unused bits inside,
         // otherwise just take the whole data block at once
         // a few select pointers (notably symbol) also have special hash values
@@ -424,7 +424,7 @@ static uintptr_t NOINLINE jl_object_id__cold(jl_datatype_t *dt, jl_value_t *v) J
     if (dt->name->mutabl) {
         // FIXME: Pinning objects that get hashed
         // until we implement address space hashing.
-        mmtk_pin_object(v);
+        PTR_PIN(v);
         return inthash((uintptr_t)v);
     }
     return immut_id_(dt, v, dt->hash);
diff --git a/src/datatype.c b/src/datatype.c
index 9f966effbc513..345bab270e912 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -67,7 +67,7 @@ JL_DLLEXPORT jl_typename_t *jl_new_typename_in(jl_sym_t *name, jl_module_t *modu
                                     jl_typename_type);
     // Typenames should be pinned since they are used as metadata, and are
     // read during scan_object
-    mmtk_pin_object(tn);
+    PTR_PIN(tn);
     tn->name = name;
     tn->module = module;
     tn->wrapper = NULL;
@@ -101,7 +101,7 @@ jl_datatype_t *jl_new_uninitialized_datatype(void)
     jl_datatype_t *t = (jl_datatype_t*)jl_gc_alloc(ct->ptls, sizeof(jl_datatype_t), jl_datatype_type);
     // Types should be pinned since they are used as metadata, and are
     // read during scan_object
-    mmtk_pin_object(t);
+    PTR_PIN(t);
     t->hash = 0;
     t->hasfreetypevars = 0;
     t->isdispatchtuple = 0;
diff --git a/src/julia.h b/src/julia.h
index 4641eff3d9839..2961e7997bb7c 100644
--- a/src/julia.h
+++ b/src/julia.h
@@ -13,8 +13,11 @@ extern int mmtk_object_is_managed_by_mmtk(void* addr);
 extern unsigned char mmtk_pin_object(void* obj);
 // FIXME: Pinning objects that get hashed in the ptrhash table
 // until we implement address space hashing.
-#define PTRHASH_PIN(key)                        \
-        mmtk_pin_object(key);                   \
+#ifdef MMTK_GC
+#define PTRHASH_PIN(key) mmtk_pin_object(key);
+#else
+#define PTRHASH_PIN(key)
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/src/julia_internal.h b/src/julia_internal.h
index e3d3fdb24cee7..f2b8c3ad7e526 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -3,6 +3,22 @@
 #ifndef JL_INTERNAL_H
 #define JL_INTERNAL_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern int mmtk_object_is_managed_by_mmtk(void* addr);
+extern unsigned char mmtk_pin_object(void* obj);
+#ifdef MMTK_GC
+#define PTR_PIN(key) mmtk_pin_object(key);
+#else
+#define PTR_PIN(key)
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
 #include "options.h"
 #include "julia_locks.h"
 #include "julia_threads.h"
@@ -532,7 +548,7 @@ STATIC_INLINE jl_gc_tracked_buffer_t *jl_gc_alloc_buf(jl_ptls_t ptls, size_t sz)
     // introspect the object to update the a->data field. To avoid doing that and
     // making scan_object much more complex we simply enforce that both owner and
     // buffers are always pinned
-    mmtk_pin_object(buf);
+    PTR_PIN(buf);
     return buf;
 }