diff --git a/lib/zip_source_winzip_aes_encode.c b/lib/zip_source_winzip_aes_encode.c
index c428c9a..4e5f753 100644
--- a/lib/zip_source_winzip_aes_encode.c
+++ b/lib/zip_source_winzip_aes_encode.c
@@ -163,7 +163,7 @@ winzip_aes_encrypt(zip_source_t *src, void *ud, void *data, zip_uint64_t length,
 		/* TODO: return partial read? */
 		return -1;
 	    }
-	    buffer_n += _zip_buffer_read(ctx->buffer, data + ret, length - (zip_uint64_t)ret);
+	    buffer_n += _zip_buffer_read(ctx->buffer, (zip_uint8_t *)data + ret, length - (zip_uint64_t)ret);
 	}
 
 	return (zip_int64_t)(buffer_n + (zip_uint64_t)ret);