diff --git a/include/mbedtls/asn1write.h b/include/mbedtls/asn1write.h
index d60ca0d..5554720 100644
--- a/include/mbedtls/asn1write.h
+++ b/include/mbedtls/asn1write.h
@@ -86,7 +86,7 @@
 
 #if defined(MBEDTLS_BIGNUM_C)
 /**
- * \brief           Write a arbitrary-precision number (#MBEDTLS_ASN1_INTEGER)
+ * \brief           Write an arbitrary-precision number (#MBEDTLS_ASN1_INTEGER)
  *                  in ASN.1 format.
  *
  * \note            This function works backwards in data buffer.