diff --git a/include/polarssl/asn1.h b/include/polarssl/asn1.h
index dc3f2fe..893292d 100644
--- a/include/polarssl/asn1.h
+++ b/include/polarssl/asn1.h
@@ -53,6 +53,8 @@
 #define POLARSSL_ERR_ASN1_LENGTH_MISMATCH                  -0x0066  /**< Actual length differs from expected length. */
 #define POLARSSL_ERR_ASN1_INVALID_DATA                     -0x0068  /**< Data is invalid. (not used) */
 #define POLARSSL_ERR_ASN1_MALLOC_FAILED                    -0x006A  /**< Memory allocation failed */
+#define POLARSSL_ERR_ASN1_BUF_TOO_SMALL                    -0x006C  /**< Buffer too small when writing ASN.1 data structure. */
+
 /* \} name */
 
 /**