diff --git a/library/des.c b/library/des.c
index 6e08cf2..16a2e74 100644
--- a/library/des.c
+++ b/library/des.c
@@ -36,11 +36,16 @@
 
 #include "polarssl/des.h"
 
+#include <string.h>
+
+#if defined(POLARSSL_SELF_TEST)
 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else
+#include <stdio.h>
 #define polarssl_printf printf
-#endif
+#endif /* POLARSSL_PLATFORM_C */
+#endif /* POLARSSL_SELF_TEST */
 
 #if !defined(POLARSSL_DES_ALT)
 
@@ -802,9 +807,6 @@
 #endif /* !POLARSSL_DES_ALT */
 
 #if defined(POLARSSL_SELF_TEST)
-
-#include <stdio.h>
-
 /*
  * DES and 3DES test vectors from:
  *