diff --git a/crypto/bio/b_print.c b/crypto/bio/b_print.c
index bbd510170..90011db54 100644
--- a/crypto/bio/b_print.c
+++ b/crypto/bio/b_print.c
@@ -56,6 +56,13 @@
  * [including the GNU Public Licence.]
  */
 
+/* disable assert() unless BIO_DEBUG has been defined */
+#ifndef BIO_DEBUG
+# ifndef NDEBUG
+#  define NDEBUG
+# endif
+#endif
+
 /* 
  * Stolen from tjh's ssl/ssl_trc.c stuff.
  */
diff --git a/crypto/bio/bss_bio.c b/crypto/bio/bss_bio.c
index d836e3bc3..27970492a 100644
--- a/crypto/bio/bss_bio.c
+++ b/crypto/bio/bss_bio.c
@@ -7,9 +7,18 @@
  * for which no specific BIO method is available.
  * See ssl/ssltest.c for some hints on how this can be used. */
 
+/* BIO_DEBUG implies BIO_PAIR_DEBUG */
+#ifdef BIO_DEBUG
+# ifndef BIO_PAIR_DEBUG
+#  define BIO_PAIR_DEBUG
+# endif
+#endif
+
+/* disable assert() unless BIO_PAIR_DEBUG has been defined */
 #ifndef BIO_PAIR_DEBUG
-# undef NDEBUG /* avoid conflicting definitions */
-# define NDEBUG
+# ifndef NDEBUG
+#  define NDEBUG
+# endif
 #endif
 
 #include <assert.h>