diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 3388c3b..2f652b7 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -183,7 +183,10 @@
     int parent_is_trusted; /* -1 if find_parent is not in progress */
 
     /* for verify_chain() */
-    mbedtls_x509_crt *child; /* non-null iff in progress */
+    enum {
+        x509_crt_rs_none,
+        x509_crt_rs_find_parent,
+    } in_progress;  /* none if no operation is in progress */
     int self_cnt;
     mbedtls_x509_crt_verify_chain ver_chain;