diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index cf18ea7517..b8d798b18c 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -1520,6 +1520,12 @@ int ssl_write_finished( ssl_context *ssl );
 
 void ssl_optimize_checksum( ssl_context *ssl, const ssl_ciphersuite_t *ciphersuite_info );
 
+#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
+    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
+    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+int ssl_psk_derive_premaster( ssl_context *ssl, key_exchange_type_t key_ex );
+#endif
+
 #if defined(POLARSSL_PK_C)
 unsigned char ssl_sig_from_pk( pk_context *pk );
 pk_type_t ssl_pk_alg_from_sig( unsigned char sig );
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 699bcb6fd4..bc67957791 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1805,8 +1805,6 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
 #if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_PSK )
     {
-        unsigned char *p = ssl->handshake->premaster;
-
         /*
          * PSK key exchange
          *
@@ -1815,35 +1813,26 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
         if( ssl->psk == NULL )
             return( POLARSSL_ERR_SSL_PRIVATE_KEY_REQUIRED );
 
-        if( sizeof(ssl->handshake->premaster) < 4 + 2 * ssl->psk_len )
-            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
-
+        i = 4;
         n = ssl->psk_identity_len;
-
-        ssl->out_msg[4] = (unsigned char)( n >> 8 );
-        ssl->out_msg[5] = (unsigned char)( n      );
-        i = 6;
+        ssl->out_msg[i++] = (unsigned char)( n >> 8 );
+        ssl->out_msg[i++] = (unsigned char)( n      );
 
         memcpy( ssl->out_msg + i, ssl->psk_identity, ssl->psk_identity_len );
+        i += ssl->psk_identity_len;
 
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        p += ssl->psk_len;
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = 4 + 2 * ssl->psk_len;
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
+        {
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
+            return( ret );
+        }
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED */
 #if defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_DHE_PSK )
     {
-        unsigned char *p = ssl->handshake->premaster;
-
         /*
          * DHE_PSK key exchange
          *
@@ -1853,24 +1842,21 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
         if( ssl->psk == NULL )
             return( POLARSSL_ERR_SSL_PRIVATE_KEY_REQUIRED );
 
-        if( sizeof(ssl->handshake->premaster) < 4 + ssl->psk_identity_len +
-                                                ssl->handshake->dhm_ctx.len )
-            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
-
         i = 4;
         n = ssl->psk_identity_len;
-        ssl->out_msg[4] = (unsigned char)( n >> 8 );
-        ssl->out_msg[5] = (unsigned char)( n      );
+        ssl->out_msg[i++] = (unsigned char)( n >> 8 );
+        ssl->out_msg[i++] = (unsigned char)( n      );
 
-        memcpy( ssl->out_msg + 6, ssl->psk_identity, ssl->psk_identity_len );
+        memcpy( ssl->out_msg + i, ssl->psk_identity, ssl->psk_identity_len );
+        i += ssl->psk_identity_len;
 
         n = ssl->handshake->dhm_ctx.len;
-        ssl->out_msg[6 + ssl->psk_identity_len] = (unsigned char)( n >> 8 );
-        ssl->out_msg[7 + ssl->psk_identity_len] = (unsigned char)( n      );
+        ssl->out_msg[i++] = (unsigned char)( n >> 8 );
+        ssl->out_msg[i++] = (unsigned char)( n      );
 
         ret = dhm_make_public( &ssl->handshake->dhm_ctx,
                                 mpi_size( &ssl->handshake->dhm_ctx.P ),
-                               &ssl->out_msg[8 + ssl->psk_identity_len], n,
+                               &ssl->out_msg[i], n,
                                 ssl->f_rng, ssl->p_rng );
         if( ret != 0 )
         {
@@ -1878,38 +1864,18 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
             return( ret );
         }
 
-        SSL_DEBUG_MPI( 3, "DHM: X ", &ssl->handshake->dhm_ctx.X  );
-        SSL_DEBUG_MPI( 3, "DHM: GX", &ssl->handshake->dhm_ctx.GX );
-
-        *(p++) = (unsigned char)( ssl->handshake->dhm_ctx.len >> 8 );
-        *(p++) = (unsigned char)( ssl->handshake->dhm_ctx.len      );
-        if( ( ret = dhm_calc_secret( &ssl->handshake->dhm_ctx,
-                                      p, &n, ssl->f_rng, ssl->p_rng ) ) != 0 )
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
         {
-            SSL_DEBUG_RET( 1, "dhm_calc_secret", ret );
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
             return( ret );
         }
-
-        SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
-
-        p += ssl->handshake->dhm_ctx.len;
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = 4 + ssl->handshake->dhm_ctx.len + ssl->psk_len;
-        n = ssl->handshake->pmslen;
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED */
 #if defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_ECDHE_PSK )
     {
-        unsigned char *p = ssl->handshake->premaster;
-        size_t zlen;
-
         /*
          * ECDHE_PSK key exchange: RFC 5489, section 2
          *
@@ -1919,9 +1885,6 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
         if( ssl->psk == NULL )
             return( POLARSSL_ERR_SSL_PRIVATE_KEY_REQUIRED );
 
-        if( sizeof(ssl->handshake->premaster) < 4 + ssl->psk_identity_len )
-            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
-
         i = 4;
         ssl->out_msg[i++] = (unsigned char)( ssl->psk_identity_len >> 8 );
         ssl->out_msg[i++] = (unsigned char)( ssl->psk_identity_len      );
@@ -1930,7 +1893,7 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
         i += ssl->psk_identity_len;
 
         ret = ecdh_make_public( &ssl->handshake->ecdh_ctx, &n,
-                                &ssl->out_msg[i], 1000,
+                                &ssl->out_msg[i], SSL_MAX_CONTENT_LEN - i,
                                 ssl->f_rng, ssl->p_rng );
         if( ret != 0 )
         {
@@ -1940,33 +1903,12 @@ static int ssl_write_client_key_exchange( ssl_context *ssl )
 
         SSL_DEBUG_ECP( 3, "ECDH: Q", &ssl->handshake->ecdh_ctx.Q );
 
-        /*
-         * PMS = struct {
-         *     opaque other_secret<0..2^16-1>;
-         *     opaque psk<0..2^16-1>;
-         * };
-         * with "other_secret" containing Z from ECDH
-         */
-        if( ( ret = ecdh_calc_secret( &ssl->handshake->ecdh_ctx, &zlen,
-                                       p + 2, POLARSSL_MPI_MAX_SIZE,
-                                       ssl->f_rng, ssl->p_rng ) ) != 0 )
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
         {
-            SSL_DEBUG_RET( 1, "ecdh_calc_secret", ret );
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
             return( ret );
         }
-
-        *(p++) = (unsigned char)( zlen >> 8 );
-        *(p++) = (unsigned char)( zlen      );
-        p += zlen;
-
-        SSL_DEBUG_MPI( 3, "ECDH: z", &ssl->handshake->ecdh_ctx.z );
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = p - ssl->handshake->premaster;
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 158877090b..f09b924672 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2022,10 +2022,9 @@ static int ssl_write_server_key_exchange( ssl_context *ssl )
         SSL_DEBUG_MSG( 2, ( "ECDH curve size: %d",
                             (int) ssl->handshake->ecdh_ctx.grp.nbits ) );
 
-        if( ( ret = ecdh_make_params( &ssl->handshake->ecdh_ctx,
-                                      &len,
-                                      p,
-                                      1000, ssl->f_rng, ssl->p_rng ) ) != 0 )
+        if( ( ret = ecdh_make_params( &ssl->handshake->ecdh_ctx, &len,
+                                      p, SSL_MAX_CONTENT_LEN - n,
+                                      ssl->f_rng, ssl->p_rng ) ) != 0 )
         {
             SSL_DEBUG_RET( 1, "ecdh_make_params", ret );
             return( ret );
@@ -2532,26 +2531,18 @@ static int ssl_parse_client_key_exchange( ssl_context *ssl )
             return( ret );
         }
 
-        // Set up the premaster secret
-        //
-        p = ssl->handshake->premaster;
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        p += ssl->psk_len;
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = 4 + 2 * ssl->psk_len;
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
+        {
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
+            return( ret );
+        }
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED */
 #if defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_DHE_PSK )
     {
-        size_t n;
         unsigned char *p = ssl->in_msg + 4;
         unsigned char *end = ssl->in_msg + ssl->in_msglen;
 
@@ -2566,38 +2557,18 @@ static int ssl_parse_client_key_exchange( ssl_context *ssl )
             return( ret );
         }
 
-        // Set up the premaster secret
-        //
-        p = ssl->handshake->premaster;
-        *(p++) = (unsigned char)( ssl->handshake->dhm_ctx.len >> 8 );
-        *(p++) = (unsigned char)( ssl->handshake->dhm_ctx.len      );
-
-        n = ssl->handshake->dhm_ctx.len;
-
-        if( ( ret = dhm_calc_secret( &ssl->handshake->dhm_ctx,
-                                      p, &n, ssl->f_rng, ssl->p_rng ) ) != 0 )
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
         {
-            SSL_DEBUG_RET( 1, "dhm_calc_secret", ret );
-            return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS );
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
+            return( ret );
         }
-
-        SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
-
-        p += ssl->handshake->dhm_ctx.len;
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = 4 + ssl->handshake->dhm_ctx.len + ssl->psk_len;
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED */
 #if defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
     if( ciphersuite_info->key_exchange == POLARSSL_KEY_EXCHANGE_ECDHE_PSK )
     {
-        size_t n;
         unsigned char *p = ssl->in_msg + 4;
         unsigned char *end = ssl->in_msg + ssl->in_msglen;
 
@@ -2616,31 +2587,12 @@ static int ssl_parse_client_key_exchange( ssl_context *ssl )
 
         SSL_DEBUG_ECP( 3, "ECDH: Qp ", &ssl->handshake->ecdh_ctx.Qp );
 
-        // Set up the premaster secret
-        //
-        p = ssl->handshake->premaster;
-
-        if( ( ret = ecdh_calc_secret( &ssl->handshake->ecdh_ctx, &n,
-                                       p + 2, POLARSSL_MPI_MAX_SIZE,
-                                       ssl->f_rng, ssl->p_rng ) ) != 0 )
+        if( ( ret = ssl_psk_derive_premaster( ssl,
+                        ciphersuite_info->key_exchange ) ) != 0 )
         {
-            SSL_DEBUG_RET( 1, "ecdh_calc_secret", ret );
+            SSL_DEBUG_RET( 1, "ssl_psk_derive_premaster", ret );
             return( ret );
         }
-
-        *(p++) = (unsigned char)( n >> 8 );
-        *(p++) = (unsigned char)( n      );
-        p += n;
-
-        SSL_DEBUG_MPI( 3, "ECDH: z", &ssl->handshake->ecdh_ctx.z );
-
-        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
-        *(p++) = (unsigned char)( ssl->psk_len      );
-        memcpy( p, ssl->psk, ssl->psk_len );
-        p += ssl->psk_len;
-
-        ssl->handshake->pmslen = 4 + n + ssl->psk_len;
-        n = ssl->handshake->pmslen;
     }
     else
 #endif /* POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d3b4ce3a09..e4ae682297 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -825,6 +825,96 @@ void ssl_calc_verify_tls_sha384( ssl_context *ssl, unsigned char hash[48] )
 #endif /* POLARSSL_SHA512_C */
 #endif /* POLARSSL_SSL_PROTO_TLS1_2 */
 
+#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED) ||                           \
+    defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED) ||                       \
+    defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+int ssl_psk_derive_premaster( ssl_context *ssl, key_exchange_type_t key_ex )
+{
+    int ret;
+    unsigned char *p = ssl->handshake->premaster;
+    unsigned char *end = p + sizeof( ssl->handshake->premaster );
+
+    /*
+     * PMS = struct {
+     *     opaque other_secret<0..2^16-1>;
+     *     opaque psk<0..2^16-1>;
+     * };
+     * with "other_secret" depending on the particular key exchange
+     */
+#if defined(POLARSSL_KEY_EXCHANGE_PSK_ENABLED)
+    if( key_ex == POLARSSL_KEY_EXCHANGE_PSK )
+    {
+        if( end - p < 2 + (int) ssl->psk_len )
+            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
+        *(p++) = (unsigned char)( ssl->psk_len >> 8 );
+        *(p++) = (unsigned char)( ssl->psk_len      );
+        p += ssl->psk_len;
+    }
+    else
+#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED */
+#if defined(POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED)
+    if( key_ex == POLARSSL_KEY_EXCHANGE_DHE_PSK )
+    {
+        size_t len = ssl->handshake->dhm_ctx.len;
+
+        if( end - p < 2 + (int) len )
+            return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
+
+        *(p++) = (unsigned char)( len >> 8 );
+        *(p++) = (unsigned char)( len );
+        if( ( ret = dhm_calc_secret( &ssl->handshake->dhm_ctx,
+                                      p, &len, ssl->f_rng, ssl->p_rng ) ) != 0 )
+        {
+            SSL_DEBUG_RET( 1, "dhm_calc_secret", ret );
+            return( ret );
+        }
+        p += len;
+
+        SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
+    }
+    else
+#endif /* POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED */
+#if defined(POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
+    if( key_ex == POLARSSL_KEY_EXCHANGE_ECDHE_PSK )
+    {
+        size_t zlen;
+
+        if( ( ret = ecdh_calc_secret( &ssl->handshake->ecdh_ctx, &zlen,
+                                       p + 2, end - (p + 2),
+                                       ssl->f_rng, ssl->p_rng ) ) != 0 )
+        {
+            SSL_DEBUG_RET( 1, "ecdh_calc_secret", ret );
+            return( ret );
+        }
+
+        *(p++) = (unsigned char)( zlen >> 8 );
+        *(p++) = (unsigned char)( zlen      );
+        p += zlen;
+
+        SSL_DEBUG_MPI( 3, "ECDH: z", &ssl->handshake->ecdh_ctx.z );
+    }
+    else
+#endif /* POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+    {
+        SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( POLARSSL_ERR_SSL_FEATURE_UNAVAILABLE );
+    }
+
+    /* opaque psk<0..2^16-1>; */
+    *(p++) = (unsigned char)( ssl->psk_len >> 8 );
+    *(p++) = (unsigned char)( ssl->psk_len      );
+    memcpy( p, ssl->psk, ssl->psk_len );
+    p += ssl->psk_len;
+
+    ssl->handshake->pmslen = p - ssl->handshake->premaster;
+
+    return( 0 );
+}
+#endif /* POLARSSL_KEY_EXCHANGE_PSK_ENABLED ||
+          POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED ||
+          POLARSSL_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
+
 #if defined(POLARSSL_SSL_PROTO_SSL3)
 /*
  * SSLv3.0 MAC functions