diff --git a/library/ecp.c b/library/ecp.c
index d9d5425..835bfa3 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -79,6 +79,8 @@
 
 #include "bn_mul.h"
 #include "ecp_invasive.h"
+#include "ecp_internal.h"
+#include "bignum_core.h"
 
 #include <string.h>
 
@@ -1029,6 +1031,20 @@
     return ret;
 }
 
+int mbedtls_ecp_quasi_reduction(mbedtls_mpi_uint *X,
+                                const mbedtls_mpi_mod_modulus *N)
+{
+    if (N->limbs == 0) {
+        return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+    }
+
+    mbedtls_mpi_uint c = mbedtls_mpi_core_sub(X, X, N->p, N->limbs);
+
+    (void) mbedtls_mpi_core_add_if(X, N->p, N->limbs, (unsigned) c);
+
+    return 0;
+}
+
 /*
  * Fast mod-p functions expect their argument to be in the 0..p^2 range.
  *