diff --git a/main.c b/main.c
index 5613bd3e12b959d7be5691bb886eb80e04df6e28..f7a28a5e564feebc03f850224b2f6f0c8fb3226a 100644
--- a/main.c
+++ b/main.c
@@ -295,6 +295,11 @@ print_config (void)
   printf ("WITH_GPU undefined\n");
 #endif
 
+#ifdef HAVE_MMAP
+  printf ("HAVE_MMAP = %d\n", HAVE_MMAP);
+#else
+  printf ("HAVE_MMAP undefined\n");
+#endif
 }
 
 /* r <- q mod N.