diff --git a/library/ecp.c b/library/ecp.c
index 3b68e8e..6a005d5 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1243,6 +1243,13 @@
     while( (N).s < 0 && mbedtls_mpi_cmp_int( &(N), 0 ) != 0 )           \
         MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &(N), &(N), &grp->P ) )
 
+#if ( defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED) && \
+      !( defined(MBEDTLS_ECP_NO_FALLBACK) && \
+         defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) && \
+         defined(MBEDTLS_ECP_ADD_MIXED_ALT) ) ) || \
+    ( defined(MBEDTLS_ECP_MONTGOMERY_ENABLED) && \
+      !( defined(MBEDTLS_ECP_NO_FALLBACK) && \
+         defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) ) )
 static inline int mbedtls_mpi_sub_mod( const mbedtls_ecp_group *grp,
                                        mbedtls_mpi *X,
                                        const mbedtls_mpi *A,
@@ -1254,6 +1261,7 @@
 cleanup:
     return( ret );
 }
+#endif /* All functions referencing mbedtls_mpi_sub_mod() are alt-implemented without fallback */
 
 /*
  * Reduce a mbedtls_mpi mod p in-place, to use after mbedtls_mpi_add_mpi and mbedtls_mpi_mul_int.
@@ -1276,6 +1284,10 @@
     return( ret );
 }
 
+#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED) && \
+    !( defined(MBEDTLS_ECP_NO_FALLBACK) && \
+       defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) && \
+       defined(MBEDTLS_ECP_ADD_MIXED_ALT) )
 static inline int mbedtls_mpi_shift_l_mod( const mbedtls_ecp_group *grp,
                                            mbedtls_mpi *X,
                                            size_t count )
@@ -1286,6 +1298,7 @@
 cleanup:
     return( ret );
 }
+#endif /* All functions referencing mbedtls_mpi_shift_l_mod() are alt-implemented without fallback */
 
 #if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
 /*