diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 4c0ac12..f4c87d3 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -43,6 +43,7 @@
 
 #include "psa/crypto.h"
 
+#include "psa_crypto_invasive.h"
 /* Include internal declarations that are useful for implementing persistently
  * stored keys. */
 #include "psa_crypto_storage.h"
@@ -155,6 +156,8 @@
 
 typedef struct
 {
+    void (* entropy_init )( mbedtls_entropy_context *ctx );
+    void (* entropy_free )( mbedtls_entropy_context *ctx );
     mbedtls_entropy_context entropy;
     mbedtls_ctr_drbg_context ctr_drbg;
     key_slot_t key_slots[PSA_KEY_SLOT_COUNT];
@@ -4437,6 +4440,17 @@
 /* Module setup */
 /****************************************************************/
 
+psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
+    void (* entropy_init )( mbedtls_entropy_context *ctx ),
+    void (* entropy_free )( mbedtls_entropy_context *ctx ) )
+{
+    if( global_data.rng_state != RNG_NOT_INITIALIZED )
+        return( PSA_ERROR_BAD_STATE );
+    global_data.entropy_init = entropy_init;
+    global_data.entropy_free = entropy_free;
+    return( PSA_SUCCESS );
+}
+
 void mbedtls_psa_crypto_free( void )
 {
     psa_key_slot_t key;
@@ -4457,7 +4471,7 @@
     if( global_data.rng_state != RNG_NOT_INITIALIZED )
     {
         mbedtls_ctr_drbg_free( &global_data.ctr_drbg );
-        mbedtls_entropy_free( &global_data.entropy );
+        global_data.entropy_free( &global_data.entropy );
     }
     /* Wipe all remaining data, including configuration.
      * In particular, this sets all state indicator to the value
@@ -4474,10 +4488,15 @@
     if( global_data.initialized != 0 )
         return( PSA_SUCCESS );
 
-    mbedtls_zeroize( &global_data, sizeof( global_data ) );
+    /* Set default configuration if
+     * mbedtls_psa_crypto_configure_entropy_sources() hasn't been called. */
+    if( global_data.entropy_init == NULL )
+        global_data.entropy_init = mbedtls_entropy_init;
+    if( global_data.entropy_free == NULL )
+        global_data.entropy_free = mbedtls_entropy_free;
 
     /* Initialize the random generator. */
-    mbedtls_entropy_init( &global_data.entropy );
+    global_data.entropy_init( &global_data.entropy );
     mbedtls_ctr_drbg_init( &global_data.ctr_drbg );
     global_data.rng_state = RNG_INITIALIZED;
     ret = mbedtls_ctr_drbg_seed( &global_data.ctr_drbg,
diff --git a/library/psa_crypto_invasive.h b/library/psa_crypto_invasive.h
new file mode 100644
index 0000000..642652a
--- /dev/null
+++ b/library/psa_crypto_invasive.h
@@ -0,0 +1,79 @@
+/**
+ * \file psa_crypto_invasive.h
+ *
+ * \brief PSA cryptography module: invasive interfaces for test only.
+ *
+ * The interfaces in this file are intended for testing purposes only.
+ * They MUST NOT be made available to clients over IPC in integrations
+ * with isolation, and they SHOULD NOT be made available in library
+ * integrations except when building the library for testing.
+ */
+/*
+ *  Copyright (C) 2018, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed 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.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+#ifndef PSA_CRYPTO_INVASIVE_H
+#define PSA_CRYPTO_INVASIVE_H
+
+#if defined(MBEDTLS_CONFIG_FILE)
+#include MBEDTLS_CONFIG_FILE
+#else
+#include "mbedtls/config.h"
+#endif
+
+#include "psa/crypto.h"
+
+#include "mbedtls/entropy.h"
+
+/** \brief Configure entropy sources.
+ *
+ * This function may only be called before a call to psa_crypto_init(),
+ * or after a call to mbedtls_psa_crypto_free() and before any
+ * subsequent call to psa_crypto_init().
+ *
+ * This function is only intended for test purposes. The functionality
+ * it provides is also useful for system integrators, but
+ * system integrators should configure entropy drivers instead of
+ * breaking through to the Mbed TLS API.
+ *
+ * \param entropy_init  Function to initialize the entropy context
+ *                      and set up the desired entropy sources.
+ *                      It is called by psa_crypto_init().
+ *                      By default this is mbedtls_entropy_init().
+ *                      This function cannot report failures directly.
+ *                      To indicate a failure, set the entropy context
+ *                      to a state where mbedtls_entropy_func() will
+ *                      return an error.
+ * \param entropy_free  Function to free the entropy context
+ *                      and associated resources.
+ *                      It is called by mbedtls_psa_crypto_free().
+ *                      By default this is mbedtls_entropy_free().
+ *
+ * \retval PSA_SUCCESS
+ *         Success.
+ * \retval PSA_ERROR_NOT_PERMITTED
+ *         The caller does not have the permission to configure
+ *         entropy sources.
+ * \retval PSA_ERROR_BAD_STATE
+ *         The library has already been initialized.
+ */
+psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
+    void (* entropy_init )( mbedtls_entropy_context *ctx ),
+    void (* entropy_free )( mbedtls_entropy_context *ctx ) );
+
+#endif /* PSA_CRYPTO_INVASIVE_H */