diff --git a/tests/suites/test_suite_ssl.data b/tests/suites/test_suite_ssl.data
index 5b670f9..14c04a8 100644
--- a/tests/suites/test_suite_ssl.data
+++ b/tests/suites/test_suite_ssl.data
@@ -31,8 +31,20 @@
 Callback buffer test: Reading from empty buffer
 test_callback_buffer:50:0:0:10:0:0:0:0:0
 
-Test mock TCP connection
-ssl_mock_tcp:
+Test mock blocking TCP connection
+ssl_mock_tcp:1:0:0
+
+Test mock non-blocking TCP connection: would not block
+ssl_mock_tcp:0:0:0
+
+Test mock non-blocking TCP connection: client would block
+ssl_mock_tcp:0:0xB509:0
+
+Test mock non-blocking TCP connection: server would block
+ssl_mock_tcp:0:0x0FB1:0
+
+Test mock non-blocking TCP connection: both peers would block
+ssl_mock_tcp:0:0x1111:0xEEEE
 
 SSL DTLS replay: initial state, seqnum 0
 ssl_dtls_replay:"":"000000000000":0
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 67ddd06..0ee6652 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -146,6 +146,7 @@
 typedef struct mbedtls_mock_socket
 {
     int status;
+    uint32_t blocking_pattern;
     mbedtls_test_buffer *input;
     mbedtls_test_buffer *output;
     struct mbedtls_mock_socket *peer;
@@ -255,6 +256,26 @@
 }
 
 /*
+ * Set the blocking pattern for the socket.
+ *
+ * For every bit of \p blocking_pattern set to one the socket will simulate a
+ * "would block" event. The bits are processed starting with the least
+ * significant bit and every call to a non-blocking I/O function consumes one.
+ *
+ * The behaviour of blocking I/O functions remains unchanged.
+ */
+int mbedtls_mock_socket_set_block( mbedtls_mock_socket* socket,
+                                   uint32_t blocking_pattern )
+{
+    if( socket == NULL )
+        return -1;
+
+    socket->blocking_pattern = blocking_pattern;
+
+    return 0;
+}
+
+/*
  * Callbacks for simulating blocking I/O over connection-oriented transport.
  */
 
@@ -279,6 +300,46 @@
 }
 
 /*
+ * Callbacks for simulating non-blocking I/O over connection-oriented transport.
+ */
+
+int mbedtls_mock_tcp_send_nb( void *ctx, const unsigned char *buf, size_t len )
+{
+    mbedtls_mock_socket *socket = (mbedtls_mock_socket*) ctx;
+
+    if( socket == NULL || socket->status != MBEDTLS_MOCK_SOCKET_CONNECTED )
+        return -1;
+
+    if( socket->blocking_pattern & 1 )
+    {
+        socket->blocking_pattern >>= 1;
+        return MBEDTLS_ERR_SSL_WANT_WRITE;
+    }
+
+    socket->blocking_pattern >>= 1;
+
+    return mbedtls_test_buffer_put( socket->output, buf, len );
+}
+
+int mbedtls_mock_tcp_recv_nb( void *ctx, unsigned char *buf, size_t len )
+{
+    mbedtls_mock_socket *socket = (mbedtls_mock_socket*) ctx;
+
+    if( socket == NULL || socket->status != MBEDTLS_MOCK_SOCKET_CONNECTED )
+        return -1;
+
+    if( socket->blocking_pattern & 1 )
+    {
+        socket->blocking_pattern >>= 1;
+        return MBEDTLS_ERR_SSL_WANT_READ;
+    }
+
+    socket->blocking_pattern >>= 1;
+
+    return mbedtls_test_buffer_get( socket->input, buf, len );
+}
+
+/*
  * Helper function setting up inverse record transformations
  * using given cipher, hash, EtM mode, authentication tag length,
  * and version.
@@ -811,7 +872,7 @@
  */
 
 /* BEGIN_CASE */
-void ssl_mock_tcp()
+void ssl_mock_tcp( int blocking, int client_pattern, int server_pattern )
 {
     enum { ROUNDS = 2 };
     enum { MSGLEN = 105 };
@@ -824,6 +885,21 @@
     int send_ret[ROUNDS];
     int recv_ret[ROUNDS];
     unsigned i, j, progress;
+    mbedtls_ssl_send_t *send;
+    mbedtls_ssl_recv_t *recv;
+    uint32_t client_block = client_pattern;
+    uint32_t server_block = server_pattern;
+
+    if( blocking == 0 )
+    {
+        send = mbedtls_mock_tcp_send_nb;
+        recv = mbedtls_mock_tcp_recv_nb;
+    }
+    else
+    {
+        send = mbedtls_mock_tcp_send_b;
+        recv = mbedtls_mock_tcp_recv_b;
+    }
 
     mbedtls_mock_socket_init( &client );
     mbedtls_mock_socket_init( &server );
@@ -839,29 +915,46 @@
     }
 
     /* Try sending or receiving on an unconnected socket */
-    TEST_ASSERT( mbedtls_mock_tcp_send_b( &client, message[0], MSGLEN ) < 0 );
-    TEST_ASSERT( mbedtls_mock_tcp_recv_b( &client, received[0], MSGLEN ) < 0 );
+    TEST_ASSERT( send( &client, message[0], MSGLEN ) < 0 );
+    TEST_ASSERT( recv( &client, received[0], MSGLEN ) < 0 );
 
     /* Make sure that sending a message takes a few  iterations. */
     TEST_ASSERT( 0 == mbedtls_mock_socket_connect( &client, &server,
                                                    MSGLEN / 5 ) );
+    TEST_ASSERT( 0 == mbedtls_mock_socket_set_block( &client, client_block ) );
+    TEST_ASSERT( 0 == mbedtls_mock_socket_set_block( &server, server_block ) );
 
     /* Send the message to the server */
     send_ret[0] = recv_ret[0] = 1;
     written[0] = read[0] = 0;
     while( send_ret[0] != 0 || recv_ret[0] != 0 )
     {
-        send_ret[0] = mbedtls_mock_tcp_send_b( &client,
-                                               message[0] + written[0],
+        send_ret[0] = send( &client, message[0] + written[0],
                                                MSGLEN - written[0] );
-        TEST_ASSERT( send_ret[0] >= 0 );
-        written[0] += send_ret[0];
 
-        recv_ret[0] = mbedtls_mock_tcp_recv_b( &server,
-                                               received[0] + read[0],
+        if( ( blocking == 0 ) && ( client_block & 1 ) )
+        {
+            TEST_ASSERT( send_ret[0] == MBEDTLS_ERR_SSL_WANT_WRITE );
+        }
+        else
+        {
+            TEST_ASSERT( send_ret[0] >= 0 );
+            written[0] += send_ret[0];
+        }
+        client_block >>= 1;
+
+        recv_ret[0] = recv( &server, received[0] + read[0],
                                                MSGLEN - read[0] );
-        TEST_ASSERT( recv_ret[0] >= 0 );
-        read[0] += recv_ret[0];
+        if( ( blocking == 0 ) && ( server_block & 1 ) )
+        {
+            TEST_ASSERT( recv_ret[0] == MBEDTLS_ERR_SSL_WANT_READ );
+        }
+        else
+        {
+            TEST_ASSERT( recv_ret[0] >= 0 );
+            read[0] += recv_ret[0];
+        }
+        server_block >>= 1;
     }
     TEST_ASSERT( memcmp( message[0], received[0], MSGLEN ) == 0 );
 
@@ -873,6 +966,10 @@
     /* Make sure that sending a message takes a few  iterations. */
     TEST_ASSERT( 0 == mbedtls_mock_socket_connect( &client, &server,
                                                    MSGLEN / 5 ) );
+    client_block = client_pattern;
+    server_block = server_pattern;
+    TEST_ASSERT( 0 == mbedtls_mock_socket_set_block( &client, client_block ) );
+    TEST_ASSERT( 0 == mbedtls_mock_socket_set_block( &server, server_block ) );
 
     /* Send the message from both sides, interleaving. */
     progress = 1;
@@ -885,38 +982,72 @@
      * of at least one byte on either side. */
     while( progress != 0 )
     {
-        send_ret[0] = mbedtls_mock_tcp_send_b( &client,
-                                               message[0] + written[0],
+        send_ret[0] = send( &client, message[0] + written[0],
                                                MSGLEN - written[0] );
-        TEST_ASSERT( send_ret[0] >= 0 );
-        written[0] += send_ret[0];
+        if( ( blocking == 0 ) && ( client_block & 1 ) )
+        {
+            TEST_ASSERT( send_ret[0] == MBEDTLS_ERR_SSL_WANT_WRITE );
+        }
+        else
+        {
+            TEST_ASSERT( send_ret[0] >= 0 );
+            written[0] += send_ret[0];
+        }
+        client_block >>= 1;
 
-        send_ret[1] = mbedtls_mock_tcp_send_b( &server,
-                                               message[1] + written[1],
+        send_ret[1] = send( &server, message[1] + written[1],
                                                MSGLEN - written[1] );
-        TEST_ASSERT( send_ret[1] >= 0 );
-        written[1] += send_ret[1];
+        if( ( blocking == 0 ) && ( server_block & 1 ) )
+        {
+            TEST_ASSERT( send_ret[1] == MBEDTLS_ERR_SSL_WANT_WRITE );
+        }
+        else
+        {
+            TEST_ASSERT( send_ret[1] >= 0 );
+            written[1] += send_ret[1];
+        }
+        server_block >>= 1;
 
-        recv_ret[0] = mbedtls_mock_tcp_recv_b( &server,
-                                               received[0] + read[0],
+        recv_ret[0] = recv( &server, received[0] + read[0],
                                                MSGLEN - read[0] );
-        TEST_ASSERT( recv_ret[0] >= 0 );
-        read[0] += recv_ret[0];
+        if( ( blocking == 0 ) && ( server_block & 1 ) )
+        {
+            TEST_ASSERT( recv_ret[0] == MBEDTLS_ERR_SSL_WANT_READ );
+        }
+        else
+        {
+            TEST_ASSERT( recv_ret[0] >= 0 );
+            read[0] += recv_ret[0];
+        }
+        server_block >>= 1;
 
-        recv_ret[1] = mbedtls_mock_tcp_recv_b( &client,
-                                               received[1] + read[1],
+        recv_ret[1] = recv( &client, received[1] + read[1],
                                                MSGLEN - read[1] );
-        TEST_ASSERT( recv_ret[1] >= 0 );
-        read[1] += recv_ret[1];
+        if( ( blocking == 0 ) && ( client_block & 1 ) )
+        {
+            TEST_ASSERT( recv_ret[1] == MBEDTLS_ERR_SSL_WANT_READ );
+        }
+        else
+        {
+            TEST_ASSERT( recv_ret[1] >= 0 );
+            read[1] += recv_ret[1];
+        }
+        client_block >>= 1;
 
         progress = 0;
         for( i = 0; i < ROUNDS; i++ )
         {
-            if( send_ret[i] > 0 )
+            if( ( send_ret[i] > 0 ) ||
+                    ( send_ret[i] == MBEDTLS_ERR_SSL_WANT_WRITE ) )
+            {
                 progress++;
+            }
 
-            if( recv_ret[i] > 0 )
+            if( ( recv_ret[i] > 0 ) ||
+                    ( recv_ret[i] == MBEDTLS_ERR_SSL_WANT_READ ) )
+            {
                 progress++;
+            }
         }
     }