diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index af649a2..96013b3 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5577,9 +5577,9 @@
     (void) mbedtls_mpi_core_add(X, X, Q, Q_limbs);
 
     /* M = B0 */
-    if (ciL > 4) {
-        M[P224_WIDTH_MIN] &= ((mbedtls_mpi_uint)-1) >> (P224_UNUSED_BITS);
-    }
+#ifdef MBEDTLS_HAVE_INT64
+    M[P224_WIDTH_MIN] &= ((mbedtls_mpi_uint)-1) >> (P224_UNUSED_BITS);
+ #endif
     memset(M + P224_WIDTH_MAX, 0, ((M_limbs - P224_WIDTH_MAX) * ciL));
 
     /* M = M + Q = B0 + B1 */