diff --git a/examples/natmod/btree/Makefile b/examples/natmod/btree/Makefile
new file mode 100644
index 000000000..d795102b4
--- /dev/null
+++ b/examples/natmod/btree/Makefile
@@ -0,0 +1,37 @@
+# Location of top-level MicroPython directory
+MPY_DIR = ../../..
+
+# Name of module (different to built-in btree so it can coexist)
+MOD = btree_$(ARCH)
+
+# Source files (.c or .py)
+SRC = btree_c.c btree_py.py
+
+# Architecture to build for (x86, x64, armv7m, xtensa, xtensawin)
+ARCH = x64
+
+BTREE_DIR = $(MPY_DIR)/lib/berkeley-db-1.xx
+BTREE_DEFS = -D__DBINTERFACE_PRIVATE=1 -Dmpool_error="(void)" -Dabort=abort_ "-Dvirt_fd_t=void*" $(BTREE_DEFS_EXTRA)
+CFLAGS += -I$(BTREE_DIR)/PORT/include
+CFLAGS += -Wno-old-style-definition -Wno-sign-compare -Wno-unused-parameter $(BTREE_DEFS)
+
+SRC += $(addprefix $(realpath $(BTREE_DIR))/,\
+	btree/bt_close.c \
+	btree/bt_conv.c \
+	btree/bt_delete.c \
+	btree/bt_get.c \
+	btree/bt_open.c \
+	btree/bt_overflow.c \
+	btree/bt_page.c \
+	btree/bt_put.c \
+	btree/bt_search.c \
+	btree/bt_seq.c \
+	btree/bt_split.c \
+	btree/bt_utils.c \
+	mpool/mpool.c \
+	)
+
+include $(MPY_DIR)/py/dynruntime.mk
+
+# btree needs gnu99 defined
+CFLAGS += -std=gnu99
diff --git a/examples/natmod/btree/btree_c.c b/examples/natmod/btree/btree_c.c
new file mode 100644
index 000000000..c8c5cef47
--- /dev/null
+++ b/examples/natmod/btree/btree_c.c
@@ -0,0 +1,148 @@
+#define MICROPY_ENABLE_DYNRUNTIME (1)
+#define MICROPY_PY_BTREE (1)
+
+#include "py/dynruntime.h"
+
+#include <unistd.h>
+
+#if !defined(__linux__)
+void *memcpy(void *dst, const void *src, size_t n) {
+    return mp_fun_table.memmove_(dst, src, n);
+}
+void *memset(void *s, int c, size_t n) {
+    return mp_fun_table.memset_(s, c, n);
+}
+#endif
+
+void *memmove(void *dest, const void *src, size_t n) {
+    return mp_fun_table.memmove_(dest, src, n);
+}
+
+void *malloc(size_t n) {
+    void *ptr = m_malloc(n);
+    return ptr;
+}
+void *realloc(void *ptr, size_t n) {
+    mp_printf(&mp_plat_print, "UNDEF %d\n", __LINE__);
+    return NULL;
+}
+void *calloc(size_t n, size_t m) {
+    void *ptr = m_malloc(n * m);
+    // memory already cleared by conservative GC
+    return ptr;
+}
+
+void free(void *ptr) {
+    m_free(ptr);
+}
+
+void abort_(void) {
+    nlr_raise(mp_obj_new_exception(mp_load_global(MP_QSTR_RuntimeError)));
+}
+
+int native_errno;
+#if defined(__linux__)
+int *__errno_location (void)
+#else
+int *__errno (void)
+#endif
+{
+    return &native_errno;
+}
+
+ssize_t mp_stream_posix_write(void *stream, const void *buf, size_t len) {
+    mp_obj_base_t* o = stream;
+    const mp_stream_p_t *stream_p = o->type->protocol;
+    mp_uint_t out_sz = stream_p->write(MP_OBJ_FROM_PTR(stream), buf, len, &native_errno);
+    if (out_sz == MP_STREAM_ERROR) {
+        return -1;
+    } else {
+        return out_sz;
+    }
+}
+
+ssize_t mp_stream_posix_read(void *stream, void *buf, size_t len) {
+    mp_obj_base_t* o = stream;
+    const mp_stream_p_t *stream_p = o->type->protocol;
+    mp_uint_t out_sz = stream_p->read(MP_OBJ_FROM_PTR(stream), buf, len, &native_errno);
+    if (out_sz == MP_STREAM_ERROR) {
+        return -1;
+    } else {
+        return out_sz;
+    }
+}
+
+off_t mp_stream_posix_lseek(void *stream, off_t offset, int whence) {
+    const mp_obj_base_t* o = stream;
+    const mp_stream_p_t *stream_p = o->type->protocol;
+    struct mp_stream_seek_t seek_s;
+    seek_s.offset = offset;
+    seek_s.whence = whence;
+    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_SEEK, (mp_uint_t)(uintptr_t)&seek_s, &native_errno);
+    if (res == MP_STREAM_ERROR) {
+        return -1;
+    }
+    return seek_s.offset;
+}
+
+int mp_stream_posix_fsync(void *stream) {
+    mp_obj_base_t* o = stream;
+    const mp_stream_p_t *stream_p = o->type->protocol;
+    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_FLUSH, 0, &native_errno);
+    if (res == MP_STREAM_ERROR) {
+        return -1;
+    }
+    return res;
+}
+
+mp_obj_type_t btree_type;
+
+#include "extmod/modbtree.c"
+
+mp_map_elem_t btree_locals_dict_table[8];
+STATIC MP_DEFINE_CONST_DICT(btree_locals_dict, btree_locals_dict_table);
+
+STATIC mp_obj_t btree_open(size_t n_args, const mp_obj_t *args) {
+    // Make sure we got a stream object
+    mp_get_stream_raise(args[0], MP_STREAM_OP_READ | MP_STREAM_OP_WRITE | MP_STREAM_OP_IOCTL);
+
+    BTREEINFO openinfo = {0};
+    openinfo.flags = mp_obj_get_int(args[1]);
+    openinfo.cachesize = mp_obj_get_int(args[2]);
+    openinfo.psize = mp_obj_get_int(args[3]);
+    openinfo.minkeypage = mp_obj_get_int(args[4]);
+    DB *db = __bt_open(MP_OBJ_TO_PTR(args[0]), &btree_stream_fvtable, &openinfo, 0);
+    if (db == NULL) {
+        mp_raise_OSError(native_errno);
+    }
+
+    return MP_OBJ_FROM_PTR(btree_new(db));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(btree_open_obj, 5, 5, btree_open);
+
+mp_obj_t mpy_init(mp_obj_fun_bc_t *self, size_t n_args, size_t n_kw, mp_obj_t *args) {
+    MP_DYNRUNTIME_INIT_ENTRY
+
+    btree_type.base.type = (void*)&mp_fun_table.type_type;
+    btree_type.name = MP_QSTR_btree;
+    btree_type.print = btree_print;
+    btree_type.getiter = btree_getiter;
+    btree_type.iternext = btree_iternext;
+    btree_type.binary_op = btree_binary_op;
+    btree_type.subscr = btree_subscr;
+    btree_locals_dict_table[0] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_close), MP_OBJ_FROM_PTR(&btree_close_obj) };
+    btree_locals_dict_table[1] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_flush), MP_OBJ_FROM_PTR(&btree_flush_obj) };
+    btree_locals_dict_table[2] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_get), MP_OBJ_FROM_PTR(&btree_get_obj) };
+    btree_locals_dict_table[3] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_put), MP_OBJ_FROM_PTR(&btree_put_obj) };
+    btree_locals_dict_table[4] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_seq), MP_OBJ_FROM_PTR(&btree_seq_obj) };
+    btree_locals_dict_table[5] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_keys), MP_OBJ_FROM_PTR(&btree_keys_obj) };
+    btree_locals_dict_table[6] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_values), MP_OBJ_FROM_PTR(&btree_values_obj) };
+    btree_locals_dict_table[7] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_items), MP_OBJ_FROM_PTR(&btree_items_obj) };
+    btree_type.locals_dict = (void*)&btree_locals_dict;
+
+    mp_store_global(MP_QSTR__open, MP_OBJ_FROM_PTR(&btree_open_obj));
+    mp_store_global(MP_QSTR_INCL, MP_OBJ_NEW_SMALL_INT(FLAG_END_KEY_INCL));
+    mp_store_global(MP_QSTR_DESC, MP_OBJ_NEW_SMALL_INT(FLAG_DESC));
+
+    MP_DYNRUNTIME_INIT_EXIT
+}
diff --git a/examples/natmod/btree/btree_py.py b/examples/natmod/btree/btree_py.py
new file mode 100644
index 000000000..bd53c084a
--- /dev/null
+++ b/examples/natmod/btree/btree_py.py
@@ -0,0 +1,3 @@
+# Implemented in Python to support keyword arguments
+def open(stream, *, flags=0, cachesize=0, pagesize=0, minkeypage=0):
+    return _open(stream, flags, cachesize, pagesize, minkeypage)