diff --git a/crypto/err/err.c b/crypto/err/err.c
index 906e3543e1..e50c6d6f9d 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -757,6 +757,8 @@ void ERR_add_error_vdata(int num, va_list args)
     n = 0;
     for (i = 0; i < num; i++) {
         a = va_arg(args, char *);
+        if (a == NULL)
+            a = "<NULL>";
         n += strlen(a);
         if (n > s) {
             s = n + 20;