diff --git a/library/constant_time.h b/library/constant_time.h
index 588181e..5a932cc 100644
--- a/library/constant_time.h
+++ b/library/constant_time.h
@@ -65,3 +65,7 @@
                                       unsigned char assign );
 
 #endif /* MBEDTLS_BIGNUM_C */
+
+void mbedtls_cf_mem_move_to_left( void *start,
+                                  size_t total,
+                                  size_t offset );