diff --git a/bl2/ext/mcuboot/os.c b/bl2/ext/mcuboot/os.c
new file mode 100644
index 0000000..0a5abbd
--- /dev/null
+++ b/bl2/ext/mcuboot/os.c
@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#include <zephyr.h>
+#include <string.h>
+
+#include "os/os_heap.h"
+
+#define MBEDTLS_CONFIG_FILE CONFIG_MBEDTLS_CFG_FILE
+#include <mbedtls/platform.h>
+
+/* D(void *os_malloc(size_t size)) */
+void *os_calloc(size_t nelem, size_t size)
+{
+    /* Note that this doesn't check for overflow.  Assume the
+     * calls only come from within the app. */
+    size_t total = nelem * size;
+    void *buf = k_malloc(total);
+    if (buf) {
+        memset(buf, 0, total);
+    }
+    return buf;
+}
+
+void os_free(void *ptr)
+{
+    k_free(ptr);
+}
+
+/*
+ * Initialize mbedtls to be able to use the local heap.
+ */
+void os_heap_init(void)
+{
+    mbedtls_platform_set_calloc_free(os_calloc, os_free);
+}