diff --git a/library/ecdh.c b/library/ecdh.c
index da95c60..204a278 100644
--- a/library/ecdh.c
+++ b/library/ecdh.c
@@ -442,8 +442,21 @@
     ECDH_VALIDATE_RET( side == MBEDTLS_ECDH_OURS ||
                        side == MBEDTLS_ECDH_THEIRS );
 
-    if( ( ret = mbedtls_ecdh_setup( ctx, key->grp.id ) ) != 0 )
-        return( ret );
+    if( ctx->grp.id == MBEDTLS_ECP_DP_NONE )
+    {
+        /* This is the first call to get_params(). Set up the context
+         * for use with the group. */
+        if( ( ret = mbedtls_ecdh_setup( ctx, key->grp.id ) ) != 0 )
+            return( ret );
+    }
+    else
+    {
+        /* This is not the first call to get_params(). Check that the
+         * current key's group is the same as the context's, which was set
+         * from the first key's group. */
+        if( ctx->grp.id != key->grp.id )
+            return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
+    }
 
 #if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
     return( ecdh_get_params_internal( ctx, key, side ) );