Fixed const correctness issues that have no impact on the ABI
diff --git a/library/error.c b/library/error.c
index d4bc277..3f71748 100644
--- a/library/error.c
+++ b/library/error.c
@@ -27,6 +27,8 @@
 
 #if defined(POLARSSL_ERROR_C)
 
+#include "polarssl/error.h"
+
 #if defined(POLARSSL_AES_C)
 #include "polarssl/aes.h"
 #endif