diff --git a/include/polarssl/ctr_drbg.h b/include/polarssl/ctr_drbg.h
index 5b20d49..83861a9 100644
--- a/include/polarssl/ctr_drbg.h
+++ b/include/polarssl/ctr_drbg.h
@@ -34,6 +34,7 @@
 #define POLARSSL_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED        -0x0034  /**< The entropy source failed. */
 #define POLARSSL_ERR_CTR_DRBG_REQUEST_TOO_BIG              -0x0036  /**< Too many random requested in single call. */
 #define POLARSSL_ERR_CTR_DRBG_INPUT_TOO_BIG                -0x0038  /**< Input too large (Entropy + additional). */
+#define POLARSSL_ERR_CTR_DRBG_FILE_IO_ERROR                -0x003A  /**< Read/write error in file. */
 
 #define CTR_DRBG_BLOCKSIZE          16      /**< Block size used by the cipher                  */
 #define CTR_DRBG_KEYSIZE            32      /**< Key size used by the cipher                    */