diff --git a/py/qstr.c b/py/qstr.c
index 848a583304..f9ca106837 100644
--- a/py/qstr.c
+++ b/py/qstr.c
@@ -122,10 +122,10 @@ void qstr_init(void) {
     #endif
 }
 
-STATIC qstr_pool_t *find_qstr(qstr *q) {
+STATIC const qstr_pool_t *find_qstr(qstr *q) {
     // search pool for this qstr
     // total_prev_len==0 in the final pool, so the loop will always terminate
-    qstr_pool_t *pool = MP_STATE_VM(last_pool);
+    const qstr_pool_t *pool = MP_STATE_VM(last_pool);
     while (*q < pool->total_prev_len) {
         pool = pool->prev;
     }
@@ -184,7 +184,7 @@ qstr qstr_find_strn(const char *str, size_t str_len) {
     mp_uint_t str_hash = qstr_compute_hash((const byte *)str, str_len);
 
     // search pools for the data
-    for (qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL; pool = pool->prev) {
+    for (const qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL; pool = pool->prev) {
         for (mp_uint_t at = 0, top = pool->len; at < top; at++) {
             if (pool->hashes[at] == str_hash && pool->lengths[at] == str_len
                 && memcmp(pool->qstrs[at], str, str_len) == 0) {
@@ -264,22 +264,22 @@ qstr qstr_from_strn(const char *str, size_t len) {
 }
 
 mp_uint_t qstr_hash(qstr q) {
-    qstr_pool_t *pool = find_qstr(&q);
+    const qstr_pool_t *pool = find_qstr(&q);
     return pool->hashes[q];
 }
 
 size_t qstr_len(qstr q) {
-    qstr_pool_t *pool = find_qstr(&q);
+    const qstr_pool_t *pool = find_qstr(&q);
     return pool->lengths[q];
 }
 
 const char *qstr_str(qstr q) {
-    qstr_pool_t *pool = find_qstr(&q);
+    const qstr_pool_t *pool = find_qstr(&q);
     return pool->qstrs[q];
 }
 
 const byte *qstr_data(qstr q, size_t *len) {
-    qstr_pool_t *pool = find_qstr(&q);
+    const qstr_pool_t *pool = find_qstr(&q);
     *len = pool->lengths[q];
     return (byte *)pool->qstrs[q];
 }
@@ -290,7 +290,7 @@ void qstr_pool_info(size_t *n_pool, size_t *n_qstr, size_t *n_str_data_bytes, si
     *n_qstr = 0;
     *n_str_data_bytes = 0;
     *n_total_bytes = 0;
-    for (qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL && pool != &CONST_POOL; pool = pool->prev) {
+    for (const qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL && pool != &CONST_POOL; pool = pool->prev) {
         *n_pool += 1;
         *n_qstr += pool->len;
         for (qstr_len_t *l = pool->lengths, *l_top = pool->lengths + pool->len; l < l_top; l++) {
@@ -310,8 +310,8 @@ void qstr_pool_info(size_t *n_pool, size_t *n_qstr, size_t *n_str_data_bytes, si
 #if MICROPY_PY_MICROPYTHON_MEM_INFO
 void qstr_dump_data(void) {
     QSTR_ENTER();
-    for (qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL && pool != &CONST_POOL; pool = pool->prev) {
-        for (const char **q = pool->qstrs, **q_top = pool->qstrs + pool->len; q < q_top; q++) {
+    for (const qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL && pool != &CONST_POOL; pool = pool->prev) {
+        for (const char *const *q = pool->qstrs, *const *q_top = pool->qstrs + pool->len; q < q_top; q++) {
             mp_printf(&mp_plat_print, "Q(%s)\n", *q);
         }
     }
diff --git a/py/qstr.h b/py/qstr.h
index 19672afc0d..ded105760c 100644
--- a/py/qstr.h
+++ b/py/qstr.h
@@ -64,7 +64,7 @@ typedef uint16_t qstr_len_t;
 #endif
 
 typedef struct _qstr_pool_t {
-    struct _qstr_pool_t *prev;
+    const struct _qstr_pool_t *prev;
     size_t total_prev_len;
     size_t alloc;
     size_t len;
diff --git a/tools/mpy-tool.py b/tools/mpy-tool.py
index 337f580b6e..58a4a75c91 100755
--- a/tools/mpy-tool.py
+++ b/tools/mpy-tool.py
@@ -883,7 +883,7 @@ def freeze_mpy(base_qstrs, raw_codes):
     print()
     print("extern const qstr_pool_t mp_qstr_const_pool;")
     print("const qstr_pool_t mp_qstr_frozen_const_pool = {")
-    print("    (qstr_pool_t*)&mp_qstr_const_pool, // previous pool")
+    print("    &mp_qstr_const_pool, // previous pool")
     print("    MP_QSTRnumber_of, // previous pool size")
     print("    %u, // allocated entries" % qstr_pool_alloc)
     print("    %u, // used entries" % len(new))