diff --git a/include/mbedtls/chachapoly.h b/include/mbedtls/chachapoly.h
index ddcd54972..ce9737c2b 100644
--- a/include/mbedtls/chachapoly.h
+++ b/include/mbedtls/chachapoly.h
@@ -183,8 +183,8 @@ int mbedtls_chachapoly_starts( mbedtls_chachapoly_context *ctx,
  *                  finished, or if the AAD has been finished.
  */
 int mbedtls_chachapoly_update_aad( mbedtls_chachapoly_context *ctx,
-                                   size_t aad_len,
-                                   const unsigned char *aad );
+                                   const unsigned char *aad,
+                                   size_t aad_len );
 
 /**
  * \brief           Thus function feeds data to be encrypted or decrypted
diff --git a/library/chachapoly.c b/library/chachapoly.c
index d599c5240..9ca21b39a 100644
--- a/library/chachapoly.c
+++ b/library/chachapoly.c
@@ -175,8 +175,8 @@ cleanup:
 }
 
 int mbedtls_chachapoly_update_aad( mbedtls_chachapoly_context *ctx,
-                                   size_t aad_len,
-                                   const unsigned char *aad )
+                                   const unsigned char *aad,
+                                   size_t aad_len )
 {
     if ( ctx == NULL )
     {
@@ -311,7 +311,7 @@ int mbedtls_chachapoly_crypt_and_tag( mbedtls_chachapoly_context *ctx,
     if ( result != 0 )
         goto cleanup;
 
-    result = mbedtls_chachapoly_update_aad( ctx, aad_len, aad );
+    result = mbedtls_chachapoly_update_aad( ctx, aad, aad_len );
     if ( result != 0 )
             goto cleanup;
 
diff --git a/library/cipher.c b/library/cipher.c
index 1827770b1..2463a6148 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -320,7 +320,7 @@ int mbedtls_cipher_update_ad( mbedtls_cipher_context_t *ctx,
             return( result );
 
         return mbedtls_chachapoly_update_aad( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
-                                                          ad_len, ad );
+                                                          ad, ad_len );
     }
 #endif