diff --git a/ChangeLog b/ChangeLog
index af7ee46e7..2c031a189 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,14 @@ mbed TLS ChangeLog (Sorted per branch, date)
 
 = mbed TLS 2.7.x branch released xxxx-xx-xx
 
+Security
+   * Make mbedtls_ecdh_get_params return an error if the second key
+     belongs to a different group from the first. Before, if an application
+     passed keys that belonged to different group, the first key's data was
+     interpreted according to the second group, which could lead to either
+     an error or a meaningless output from mbedtls_ecdh_get_params. In the
+     latter case, this could expose at most 5 bits of the private key.
+
 Bugfix
    * Server's RSA certificate in certs.c was SHA-1 signed. In the default
      mbedTLS configuration only SHA-2 signed certificates are accepted.
diff --git a/library/ecdh.c b/library/ecdh.c
index 61380b693..75630bd35 100644
--- a/library/ecdh.c
+++ b/library/ecdh.c
@@ -179,8 +179,20 @@ int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypai
 {
     int ret;
 
-    if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 )
-        return( ret );
+    if( ctx->grp.id == MBEDTLS_ECP_DP_NONE )
+    {
+        /* This is the first call to get_params(). Copy the group information
+         * into the context. */
+        if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 )
+            return( ret );
+    }
+    else
+    {
+        /* This is not the first call to get_params(). Check that the group
+         * is the same as the first time. */
+        if( ctx->grp.id != key->grp.id )
+            return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
+    }
 
     /* If it's not our key, just import the public part as Qp */
     if( side == MBEDTLS_ECDH_THEIRS )
diff --git a/tests/suites/test_suite_ecdh.data b/tests/suites/test_suite_ecdh.data
index f7119de41..4ed32219b 100644
--- a/tests/suites/test_suite_ecdh.data
+++ b/tests/suites/test_suite_ecdh.data
@@ -37,3 +37,19 @@ ecdh_exchange:MBEDTLS_ECP_DP_SECP192R1
 ECDH exchange #2
 depends_on:MBEDTLS_ECP_DP_SECP521R1_ENABLED
 ecdh_exchange:MBEDTLS_ECP_DP_SECP521R1
+
+ECDH calc_secret: ours first, SECP256R1 (RFC 5903)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecdh_exchange_calc_secret:MBEDTLS_ECP_DP_SECP256R1:"c6ef9c5d78ae012a011164acb397ce2088685d8f06bf9be0b283ab46476bee53":"04dad0b65394221cf9b051e1feca5787d098dfe637fc90b9ef945d0c37725811805271a0461cdb8252d61f1c456fa3e59ab1f45b33accf5f58389e0577b8990bb3":0:"d6840f6b42f6edafd13116e0e12565202fef8e9ece7dce03812464d04b9442de"
+
+ECDH calc_secret: theirs first, SECP256R1 (RFC 5903)
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+ecdh_exchange_calc_secret:MBEDTLS_ECP_DP_SECP256R1:"c6ef9c5d78ae012a011164acb397ce2088685d8f06bf9be0b283ab46476bee53":"04dad0b65394221cf9b051e1feca5787d098dfe637fc90b9ef945d0c37725811805271a0461cdb8252d61f1c456fa3e59ab1f45b33accf5f58389e0577b8990bb3":1:"d6840f6b42f6edafd13116e0e12565202fef8e9ece7dce03812464d04b9442de"
+
+ECDH get_params with mismatched groups: our BP256R1, their SECP256R1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_BP256R1_ENABLED
+ecdh_exchange_get_params_fail:MBEDTLS_ECP_DP_BP256R1:"1234567812345678123456781234567812345678123456781234567812345678":MBEDTLS_ECP_DP_SECP256R1:"04dad0b65394221cf9b051e1feca5787d098dfe637fc90b9ef945d0c37725811805271a0461cdb8252d61f1c456fa3e59ab1f45b33accf5f58389e0577b8990bb3":0:MBEDTLS_ERR_ECP_BAD_INPUT_DATA
+
+ECDH get_params with mismatched groups: their SECP256R1, our BP256R1
+depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_BP256R1_ENABLED
+ecdh_exchange_get_params_fail:MBEDTLS_ECP_DP_BP256R1:"1234567812345678123456781234567812345678123456781234567812345678":MBEDTLS_ECP_DP_SECP256R1:"04dad0b65394221cf9b051e1feca5787d098dfe637fc90b9ef945d0c37725811805271a0461cdb8252d61f1c456fa3e59ab1f45b33accf5f58389e0577b8990bb3":1:MBEDTLS_ERR_ECP_BAD_INPUT_DATA
diff --git a/tests/suites/test_suite_ecdh.function b/tests/suites/test_suite_ecdh.function
index 4c6a97baf..0645ce798 100644
--- a/tests/suites/test_suite_ecdh.function
+++ b/tests/suites/test_suite_ecdh.function
@@ -1,5 +1,47 @@
 /* BEGIN_HEADER */
 #include "mbedtls/ecdh.h"
+
+static int load_public_key( int grp_id, const char *point_str,
+                            mbedtls_ecp_keypair *ecp )
+{
+    int ok = 0;
+    unsigned char point_buf[MBEDTLS_ECP_MAX_PT_LEN];
+    size_t point_len = unhexify( point_buf, point_str );
+
+    TEST_ASSERT( mbedtls_ecp_group_load( &ecp->grp, grp_id ) == 0 );
+    TEST_ASSERT( mbedtls_ecp_point_read_binary( &ecp->grp,
+                                                &ecp->Q,
+                                                point_buf,
+                                                point_len ) == 0 );
+    TEST_ASSERT( mbedtls_ecp_check_pubkey( &ecp->grp,
+                                           &ecp->Q ) == 0 );
+    ok = 1;
+exit:
+    return( ok );
+}
+
+static int load_private_key( int grp_id, const char *private_key_str,
+                             mbedtls_ecp_keypair *ecp,
+                             rnd_pseudo_info *rnd_info )
+{
+    int ok = 0;
+    unsigned char private_key_buf[MBEDTLS_ECP_MAX_BYTES];
+    size_t private_key_len = unhexify( private_key_buf, private_key_str );
+
+    TEST_ASSERT( mbedtls_ecp_group_load( &ecp->grp, grp_id ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_read_binary( &ecp->d,
+                                          private_key_buf,
+                                          private_key_len ) == 0 );
+    TEST_ASSERT( mbedtls_ecp_check_privkey( &ecp->grp, &ecp->d ) == 0 );
+    /* Calculate the public key from the private key. */
+    TEST_ASSERT( mbedtls_ecp_mul( &ecp->grp, &ecp->Q, &ecp->d,
+                                  &ecp->grp.G,
+                                  &rnd_pseudo_rand, rnd_info ) == 0 );
+    ok = 1;
+exit:
+    return( ok );
+}
+
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -158,3 +200,111 @@ exit:
     mbedtls_ecdh_free( &cli );
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void ecdh_exchange_calc_secret( int grp_id,
+                                char *our_private_key,
+                                char *their_point,
+                                int ours_first,
+                                char *expected_str )
+{
+    rnd_pseudo_info rnd_info;
+    unsigned char expected_buf[MBEDTLS_ECP_MAX_BYTES];
+    size_t expected_len;
+    mbedtls_ecp_keypair our_key;
+    mbedtls_ecp_keypair their_key;
+    mbedtls_ecdh_context ecdh;
+    unsigned char shared_secret[MBEDTLS_ECP_MAX_BYTES];
+    size_t shared_secret_length = 0;
+
+    memset( &rnd_info, 0x00, sizeof( rnd_pseudo_info ) );
+    mbedtls_ecdh_init( &ecdh );
+    mbedtls_ecp_keypair_init( &our_key );
+    mbedtls_ecp_keypair_init( &their_key );
+
+    expected_len = unhexify( expected_buf, expected_str );
+
+    if( ! load_private_key( grp_id, our_private_key, &our_key, &rnd_info ) )
+        goto exit;
+    if( ! load_public_key( grp_id, their_point, &their_key ) )
+        goto exit;
+
+    /* Import the keys to the ECDH calculation. */
+    if( ours_first )
+    {
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &our_key, MBEDTLS_ECDH_OURS ) == 0 );
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &their_key, MBEDTLS_ECDH_THEIRS ) == 0 );
+    }
+    else
+    {
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &their_key, MBEDTLS_ECDH_THEIRS ) == 0 );
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &our_key, MBEDTLS_ECDH_OURS ) == 0 );
+    }
+
+    /* Perform the ECDH calculation. */
+    TEST_ASSERT( mbedtls_ecdh_calc_secret(
+                     &ecdh,
+                     &shared_secret_length,
+                     shared_secret, sizeof( shared_secret ),
+                     &rnd_pseudo_rand, &rnd_info ) == 0 );
+    TEST_ASSERT( shared_secret_length == expected_len );
+    TEST_ASSERT( memcmp( expected_buf, shared_secret,
+                         shared_secret_length ) == 0 );
+
+exit:
+    mbedtls_ecdh_free( &ecdh );
+    mbedtls_ecp_keypair_free( &our_key );
+    mbedtls_ecp_keypair_free( &their_key );
+}
+/* END_CASE */
+
+/* BEGIN_CASE */
+void ecdh_exchange_get_params_fail( int our_grp_id,
+                                    char *our_private_key,
+                                    int their_grp_id,
+                                    char *their_point,
+                                    int ours_first,
+                                    int expected_ret )
+{
+    rnd_pseudo_info rnd_info;
+    mbedtls_ecp_keypair our_key;
+    mbedtls_ecp_keypair their_key;
+    mbedtls_ecdh_context ecdh;
+
+    memset( &rnd_info, 0x00, sizeof( rnd_pseudo_info ) );
+    mbedtls_ecdh_init( &ecdh );
+    mbedtls_ecp_keypair_init( &our_key );
+    mbedtls_ecp_keypair_init( &their_key );
+
+    if( ! load_private_key( our_grp_id, our_private_key, &our_key, &rnd_info ) )
+        goto exit;
+    if( ! load_public_key( their_grp_id, their_point, &their_key ) )
+        goto exit;
+
+    if( ours_first )
+    {
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &our_key, MBEDTLS_ECDH_OURS ) == 0 );
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &their_key, MBEDTLS_ECDH_THEIRS ) ==
+                     expected_ret );
+    }
+    else
+    {
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &their_key, MBEDTLS_ECDH_THEIRS ) == 0 );
+        TEST_ASSERT( mbedtls_ecdh_get_params(
+                         &ecdh, &our_key, MBEDTLS_ECDH_OURS ) ==
+                     expected_ret );
+    }
+
+exit:
+    mbedtls_ecdh_free( &ecdh );
+    mbedtls_ecp_keypair_free( &our_key );
+    mbedtls_ecp_keypair_free( &their_key );
+}
+/* END_CASE */