diff --git a/py/qstr.h b/py/qstr.h
index fa634f90b0..a463b67a18 100644
--- a/py/qstr.h
+++ b/py/qstr.h
@@ -93,7 +93,7 @@ void qstr_pool_info(size_t *n_pool, size_t *n_qstr, size_t *n_str_data_bytes, si
 void qstr_dump_data(void);
 
 #if MICROPY_ROM_TEXT_COMPRESSION
-void mp_decompress_rom_string(byte *dst, mp_rom_error_text_t src);
+void mp_decompress_rom_string(byte *dst, const mp_rom_error_text_t src);
 #define MP_IS_COMPRESSED_ROM_STRING(s) (*(byte *)(s) == 0xff)
 #endif