diff --git a/testbn.c b/testbn.c
index 55471bd2..15f3b980 100644
--- a/testbn.c
+++ b/testbn.c
@@ -12,6 +12,7 @@
 #include <ctype.h>
 
 #include "ssh.h"
+#include "sshbn.h"
 
 void modalfatalbox(const char *p, ...)
 {
@@ -38,6 +39,8 @@ int main(int argc, char **argv)
     int line = 0;
     int passes = 0, fails = 0;
 
+    printf("BIGNUM_INT_BITS = %d\n", (int)BIGNUM_INT_BITS);
+
     while ((buf = fgetline(stdin)) != NULL) {
         int maxlen = strlen(buf);
         unsigned char *data = snewn(maxlen, unsigned char);