- Only include dependencies when required

diff --git a/library/md_wrap.c b/library/md_wrap.c
index 64d8bb6..f276db5 100644
--- a/library/md_wrap.c
+++ b/library/md_wrap.c
@@ -32,12 +32,30 @@
 #if defined(POLARSSL_MD_C)
 
 #include "polarssl/md_wrap.h"
+
+#if defined(POLARSSL_MD2_C)
 #include "polarssl/md2.h"
+#endif
+
+#if defined(POLARSSL_MD4_C)
 #include "polarssl/md4.h"
+#endif
+
+#if defined(POLARSSL_MD5_C)
 #include "polarssl/md5.h"
+#endif
+
+#if defined(POLARSSL_SHA1_C)
 #include "polarssl/sha1.h"
+#endif
+
+#if defined(POLARSSL_SHA2_C)
 #include "polarssl/sha2.h"
+#endif
+
+#if defined(POLARSSL_SHA4_C)
 #include "polarssl/sha4.h"
+#endif
 
 #include <stdlib.h>