diff --git a/library/constant_time.h b/library/constant_time.h
index 3c18b4e..973e856 100644
--- a/library/constant_time.h
+++ b/library/constant_time.h
@@ -52,3 +52,6 @@
                                  const mbedtls_mpi_uint y );
 
 #endif /* MBEDTLS_BIGNUM_C */
+
+unsigned mbedtls_cf_uint_if( unsigned cond, unsigned if1, unsigned if0 );
+