diff --git a/library/ecp.c b/library/ecp.c
index 0212069..ba6e8f3 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1464,7 +1464,10 @@
     return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
 #else
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi T1, T2, T3, T4, X, Y, Z;
+    mbedtls_mpi T1, T2, T3, T4;
+    mbedtls_mpi * const X = &R->X;
+    mbedtls_mpi * const Y = &R->Y;
+    mbedtls_mpi * const Z = &R->Z;
 
     /*
      * Trivial cases: P == 0 or Q == 0 (case 1)
@@ -1482,7 +1485,6 @@
         return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
 
     mbedtls_mpi_init( &T1 ); mbedtls_mpi_init( &T2 ); mbedtls_mpi_init( &T3 ); mbedtls_mpi_init( &T4 );
-    mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y ); mbedtls_mpi_init( &Z );
 
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T1,  &P->Z,  &P->Z ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T2,  &T1,    &P->Z ) );
@@ -1506,28 +1508,23 @@
         }
     }
 
-    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &Z,   &P->Z,  &T1   ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, Z,    &P->Z,  &T1   ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T3,  &T1,    &T1   ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T4,  &T3,    &T1   ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T3,  &T3,    &P->X ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &T1, &T3 ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l_mod( grp, &T1,  1     ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &X,   &T2,    &T2   ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &X,   &X,     &T1   ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &X,   &X,     &T4   ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &T3,  &T3,    &X    ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, X,    &T2,    &T2   ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, X,    X,      &T1   ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, X,    X,      &T4   ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &T3,  &T3,    X     ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T3,  &T3,    &T2   ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &T4,  &T4,    &P->Y ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, &Y,   &T3,    &T4   ) );
-
-    MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->X, &X ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Y, &Y ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &R->Z, &Z ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mod( grp, Y,    &T3,    &T4   ) );
 
 cleanup:
 
     mbedtls_mpi_free( &T1 ); mbedtls_mpi_free( &T2 ); mbedtls_mpi_free( &T3 ); mbedtls_mpi_free( &T4 );
-    mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &Z );
 
     return( ret );
 #endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT) */