diff --git a/include/mbedtls/poly1305.h b/include/mbedtls/poly1305.h
index c2e2655e7..19f523774 100644
--- a/include/mbedtls/poly1305.h
+++ b/include/mbedtls/poly1305.h
@@ -121,8 +121,8 @@ int mbedtls_poly1305_starts( mbedtls_poly1305_context *ctx,
  *                  if ctx or input are NULL.
  */
 int mbedtls_poly1305_update( mbedtls_poly1305_context *ctx,
-                             size_t ilen,
-                             const unsigned char *input );
+                             const unsigned char *input,
+                             size_t ilen );
 
 /**
  * \brief           This function generates the Poly1305 Message
@@ -158,8 +158,8 @@ int mbedtls_poly1305_finish( mbedtls_poly1305_context *ctx,
  *                  if key, input, or mac are NULL.
  */
 int mbedtls_poly1305_mac( const unsigned char key[32],
-                          size_t ilen,
                           const unsigned char *input,
+                          size_t ilen,
                           unsigned char mac[16] );
 
 /**
diff --git a/library/chachapoly.c b/library/chachapoly.c
index 0dba5ed91..d599c5240 100644
--- a/library/chachapoly.c
+++ b/library/chachapoly.c
@@ -66,8 +66,8 @@ static void mbedtls_chachapoly_pad_aad( mbedtls_chachapoly_context *ctx )
     {
         memset( zeroes, 0, sizeof( zeroes ) );
         (void) mbedtls_poly1305_update( &ctx->poly1305_ctx,
-                                        16U - partial_block_len,
-                                        zeroes );
+                                        zeroes,
+                                        16U - partial_block_len );
     }
 }
 
@@ -85,8 +85,8 @@ static void mbedtls_chachapoly_pad_ciphertext( mbedtls_chachapoly_context *ctx )
     {
         memset( zeroes, 0, sizeof( zeroes ) );
         (void) mbedtls_poly1305_update( &ctx->poly1305_ctx,
-                                        16U - partial_block_len,
-                                        zeroes );
+                                        zeroes,
+                                        16U - partial_block_len );
     }
 }
 
@@ -194,7 +194,7 @@ int mbedtls_chachapoly_update_aad( mbedtls_chachapoly_context *ctx,
 
     ctx->aad_len += aad_len;
 
-    return( mbedtls_poly1305_update( &ctx->poly1305_ctx, aad_len, aad ) );
+    return( mbedtls_poly1305_update( &ctx->poly1305_ctx, aad, aad_len ) );
 }
 
 int mbedtls_chachapoly_update( mbedtls_chachapoly_context *ctx,
@@ -233,11 +233,11 @@ int mbedtls_chachapoly_update( mbedtls_chachapoly_context *ctx,
          *       above, we can safety ignore the return value.
          */
         (void) mbedtls_chacha20_update( &ctx->chacha20_ctx, len, input, output );
-        (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, len, output );
+        (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, output, len );
     }
     else /* DECRYPT */
     {
-        (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, len, input );
+        (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, input, len );
         (void) mbedtls_chacha20_update( &ctx->chacha20_ctx, len, input, output );
     }
 
@@ -289,7 +289,7 @@ int mbedtls_chachapoly_finish( mbedtls_chachapoly_context *ctx,
     len_block[14] = (unsigned char) ( ctx->ciphertext_len >> 48 );
     len_block[15] = (unsigned char) ( ctx->ciphertext_len >> 56 );
 
-    (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, 16U, len_block );
+    (void) mbedtls_poly1305_update( &ctx->poly1305_ctx, len_block, 16U );
     (void) mbedtls_poly1305_finish( &ctx->poly1305_ctx, mac );
 
     return( 0 );
diff --git a/library/poly1305.c b/library/poly1305.c
index 66f932c4f..14c362d58 100644
--- a/library/poly1305.c
+++ b/library/poly1305.c
@@ -285,8 +285,8 @@ int mbedtls_poly1305_starts( mbedtls_poly1305_context *ctx,
 }
 
 int mbedtls_poly1305_update( mbedtls_poly1305_context *ctx,
-                             size_t ilen,
-                             const unsigned char* input )
+                             const unsigned char *input,
+                             size_t ilen )
 {
     size_t offset    = 0U;
     size_t remaining = ilen;
@@ -391,9 +391,9 @@ int mbedtls_poly1305_finish( mbedtls_poly1305_context *ctx,
 }
 
 int mbedtls_poly1305_mac( const unsigned char key[32],
-                           size_t ilen,
-                           const unsigned char *input,
-                           unsigned char mac[16] )
+                          const unsigned char *input,
+                          size_t ilen,
+                          unsigned char mac[16] )
 {
     mbedtls_poly1305_context ctx;
     int result;
@@ -404,7 +404,7 @@ int mbedtls_poly1305_mac( const unsigned char key[32],
     if ( result != 0 )
         goto cleanup;
 
-    result = mbedtls_poly1305_update( &ctx, ilen, input );
+    result = mbedtls_poly1305_update( &ctx, input, ilen );
     if ( result != 0 )
         goto cleanup;
 
@@ -496,8 +496,8 @@ int mbedtls_poly1305_self_test( int verbose )
         }
 
         result = mbedtls_poly1305_mac( test_keys[i],
-                                       test_data_len[i],
                                        test_data[i],
+                                       test_data_len[i],
                                        mac );
         if ( result != 0 )
         {
diff --git a/programs/test/benchmark.c b/programs/test/benchmark.c
index c41966586..17f9d0e27 100644
--- a/programs/test/benchmark.c
+++ b/programs/test/benchmark.c
@@ -538,7 +538,7 @@ int main( int argc, char *argv[] )
 #if defined(MBEDTLS_POLY1305_C)
     if ( todo.poly1305 )
     {
-        TIME_AND_TSC( "Poly1305", mbedtls_poly1305_mac( buf, BUFSIZE, buf, buf ) );
+        TIME_AND_TSC( "Poly1305", mbedtls_poly1305_mac( buf, buf, BUFSIZE, buf ) );
     }
 #endif
 
diff --git a/tests/suites/test_suite_poly1305.function b/tests/suites/test_suite_poly1305.function
index af69a0312..a633c2baa 100644
--- a/tests/suites/test_suite_poly1305.function
+++ b/tests/suites/test_suite_poly1305.function
@@ -20,7 +20,7 @@ void mbedtls_poly1305( char *hex_key_string, char *hex_mac_string, char *hex_src
     src_len = unhexify( src_str, hex_src_string );
     unhexify( key, hex_key_string );
 
-    mbedtls_poly1305_mac( key, src_len, src_str, mac );
+    mbedtls_poly1305_mac( key, src_str, src_len, mac );
     hexify( mac_str, mac, 16 );
 
     TEST_ASSERT( strcmp( (char *) mac_str, hex_mac_string ) == 0 );