diff --git a/auto_tests/file_saving_test.c b/auto_tests/file_saving_test.c
index a5ba7e1f..13a98280 100644
--- a/auto_tests/file_saving_test.c
+++ b/auto_tests/file_saving_test.c
@@ -82,6 +82,8 @@ static void load_data_decrypted(void)
     int64_t size = ftell(f);
     fseek(f, 0, SEEK_SET);
 
+    ck_assert_msg(0 <= size && size <= SIZE_MAX, "file size out of range");
+
     uint8_t *cipher = (uint8_t *)malloc(size);
     uint8_t *clear = (uint8_t *)malloc(size - TOX_PASS_ENCRYPTION_EXTRA_LENGTH);
     size_t read_value = fread(cipher, sizeof(*cipher), size, f);