diff --git a/include/mbedtls/md_wrap.h b/include/mbedtls/md_wrap.h
index 6fe377e..e0c6354 100644
--- a/include/mbedtls/md_wrap.h
+++ b/include/mbedtls/md_wrap.h
@@ -54,6 +54,9 @@
     /** Output length of the digest function */
     int size;
 
+    /** Block length of the digest function */
+    int block_size;
+
     /** Digest initialisation function */
     void (*starts_func)( void *ctx );