diff --git a/ports/stm32/pin.c b/ports/stm32/pin.c
index a8068d899..d032d9914 100644
--- a/ports/stm32/pin.c
+++ b/ports/stm32/pin.c
@@ -214,14 +214,14 @@ STATIC void pin_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t
         mp_print_str(print, qstr_str(mode_qst));
 
         // pull mode
-        qstr pull_qst = MP_QSTR_NULL;
+        qstr pull_qst = MP_QSTRnull;
         uint32_t pull = pin_get_pull(self);
         if (pull == GPIO_PULLUP) {
             pull_qst = MP_QSTR_PULL_UP;
         } else if (pull == GPIO_PULLDOWN) {
             pull_qst = MP_QSTR_PULL_DOWN;
         }
-        if (pull_qst != MP_QSTR_NULL) {
+        if (pull_qst != MP_QSTRnull) {
             mp_printf(print, ", pull=Pin.%q", pull_qst);
         }
 
diff --git a/ports/unix/coverage-frzmpy/frzqstr.py b/ports/unix/coverage-frzmpy/frzqstr.py
new file mode 100644
index 000000000..051f2a9c1
--- /dev/null
+++ b/ports/unix/coverage-frzmpy/frzqstr.py
@@ -0,0 +1,3 @@
+# Checks for regression on MP_QSTR_NULL
+def returns_NULL():
+    return "NULL"
diff --git a/py/compile.c b/py/compile.c
index a8ec0bf11..90d1bfd13 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -1205,7 +1205,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
         // do the import
         qstr dummy_q;
         do_import_name(comp, pn_import_source, &dummy_q);
-        EMIT_ARG(import, MP_QSTR_NULL, MP_EMIT_IMPORT_STAR);
+        EMIT_ARG(import, MP_QSTRnull, MP_EMIT_IMPORT_STAR);
 
     } else {
         EMIT_ARG(load_const_small_int, import_level);
@@ -2823,7 +2823,7 @@ STATIC void compile_scope_func_lambda_param(compiler_t *comp, mp_parse_node_t pn
         return;
     }
 
-    qstr param_name = MP_QSTR_NULL;
+    qstr param_name = MP_QSTRnull;
     uint param_flag = ID_FLAG_IS_PARAM;
     mp_parse_node_struct_t *pns = NULL;
     if (MP_PARSE_NODE_IS_ID(pn)) {
@@ -2882,7 +2882,7 @@ STATIC void compile_scope_func_lambda_param(compiler_t *comp, mp_parse_node_t pn
         }
     }
 
-    if (param_name != MP_QSTR_NULL) {
+    if (param_name != MP_QSTRnull) {
         id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, param_name, ID_INFO_KIND_UNDECIDED);
         if (id_info->kind != ID_INFO_KIND_UNDECIDED) {
             compile_syntax_error(comp, pn, "argument name reused");
diff --git a/py/makeqstrdata.py b/py/makeqstrdata.py
index 163b7fce7..7799be0a9 100644
--- a/py/makeqstrdata.py
+++ b/py/makeqstrdata.py
@@ -339,7 +339,7 @@ def print_qstr_data(qcfgs, qstrs):
     print('')
 
     # add NULL qstr with no hash or data
-    print('QDEF(MP_QSTR_NULL, (const byte*)"%s%s" "")' % ('\\x00' * cfg_bytes_hash, '\\x00' * cfg_bytes_len))
+    print('QDEF(MP_QSTRnull, (const byte*)"%s%s" "")' % ('\\x00' * cfg_bytes_hash, '\\x00' * cfg_bytes_len))
 
     # go through each qstr and print it out
     for order, ident, qstr in sorted(qstrs.values(), key=lambda x: x[0]):
diff --git a/py/moduerrno.c b/py/moduerrno.c
index de66c941b..0e0a3f008 100644
--- a/py/moduerrno.c
+++ b/py/moduerrno.c
@@ -104,7 +104,7 @@ qstr mp_errno_to_str(mp_obj_t errno_val) {
     // We have the errorcode dict so can do a lookup using the hash map
     mp_map_elem_t *elem = mp_map_lookup((mp_map_t*)&errorcode_dict.map, errno_val, MP_MAP_LOOKUP);
     if (elem == NULL) {
-        return MP_QSTR_NULL;
+        return MP_QSTRnull;
     } else {
         return MP_OBJ_QSTR_VALUE(elem->value);
     }
@@ -115,7 +115,7 @@ qstr mp_errno_to_str(mp_obj_t errno_val) {
             return MP_OBJ_QSTR_VALUE(mp_module_uerrno_globals_table[i].key);
         }
     }
-    return MP_QSTR_NULL;
+    return MP_QSTRnull;
     #endif
 }
 
diff --git a/py/obj.c b/py/obj.c
index 1797ee56b..4588d896a 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -93,7 +93,7 @@ void mp_obj_print_exception(const mp_print_t *print, mp_obj_t exc) {
 #endif
                 // the block name can be NULL if it's unknown
                 qstr block = values[i + 2];
-                if (block == MP_QSTR_NULL) {
+                if (block == MP_QSTRnull) {
                     mp_print_str(print, "\n");
                 } else {
                     mp_printf(print, ", in %q\n", block);
diff --git a/py/objexcept.c b/py/objexcept.c
index 7e3fdcc27..dadbe98ae 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -121,7 +121,7 @@ void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kin
             // try to provide a nice OSError error message
             if (o->base.type == &mp_type_OSError && mp_obj_is_small_int(o->args->items[0])) {
                 qstr qst = mp_errno_to_str(o->args->items[0]);
-                if (qst != MP_QSTR_NULL) {
+                if (qst != MP_QSTRnull) {
                     mp_printf(print, "[Errno " INT_FMT "] %q", MP_OBJ_SMALL_INT_VALUE(o->args->items[0]), qst);
                     return;
                 }
diff --git a/py/objstr.c b/py/objstr.c
index 1047ea94c..882436363 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -169,7 +169,7 @@ mp_obj_t mp_obj_str_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_
 
                 // Check if a qstr with this data already exists
                 qstr q = qstr_find_strn((const char*)str_data, str_len);
-                if (q != MP_QSTR_NULL) {
+                if (q != MP_QSTRnull) {
                     return MP_OBJ_NEW_QSTR(q);
                 }
 
@@ -2042,7 +2042,7 @@ mp_obj_t mp_obj_new_str_from_vstr(const mp_obj_type_t *type, vstr_t *vstr) {
     // if not a bytes object, look if a qstr with this data already exists
     if (type == &mp_type_str) {
         qstr q = qstr_find_strn(vstr->buf, vstr->len);
-        if (q != MP_QSTR_NULL) {
+        if (q != MP_QSTRnull) {
             vstr_clear(vstr);
             vstr->alloc = 0;
             return MP_OBJ_NEW_QSTR(q);
@@ -2067,7 +2067,7 @@ mp_obj_t mp_obj_new_str_from_vstr(const mp_obj_type_t *type, vstr_t *vstr) {
 
 mp_obj_t mp_obj_new_str(const char* data, size_t len) {
     qstr q = qstr_find_strn(data, len);
-    if (q != MP_QSTR_NULL) {
+    if (q != MP_QSTRnull) {
         // qstr with this data already exists
         return MP_OBJ_NEW_QSTR(q);
     } else {
diff --git a/py/objtype.c b/py/objtype.c
index 318c7b9a3..236c79e6a 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -460,7 +460,7 @@ STATIC mp_obj_t instance_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 }
 
 // Binary-op enum values not listed here will have the default value of 0 in the
-// table, corresponding to MP_QSTR_NULL, and are therefore unsupported (a lookup will
+// table, corresponding to MP_QSTRnull, and are therefore unsupported (a lookup will
 // fail).  They can be added at the expense of code size for the qstr.
 // Qstrs for special methods are guaranteed to have a small value, so we use byte
 // type to represent them.
diff --git a/py/parse.c b/py/parse.c
index 254dbc7ba..82b5413e5 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -502,7 +502,7 @@ STATIC void push_result_token(parser_t *parser, uint8_t rule_id) {
     } else if (lex->tok_kind == MP_TOKEN_STRING || lex->tok_kind == MP_TOKEN_BYTES) {
         // Don't automatically intern all strings/bytes.  doc strings (which are usually large)
         // will be discarded by the compiler, and so we shouldn't intern them.
-        qstr qst = MP_QSTR_NULL;
+        qstr qst = MP_QSTRnull;
         if (lex->vstr.len <= MICROPY_ALLOC_PARSE_INTERN_STRING_LEN) {
             // intern short strings
             qst = qstr_from_strn(lex->vstr.buf, lex->vstr.len);
@@ -510,7 +510,7 @@ STATIC void push_result_token(parser_t *parser, uint8_t rule_id) {
             // check if this string is already interned
             qst = qstr_find_strn(lex->vstr.buf, lex->vstr.len);
         }
-        if (qst != MP_QSTR_NULL) {
+        if (qst != MP_QSTRnull) {
             // qstr exists, make a leaf node
             pn = mp_parse_node_new_leaf(lex->tok_kind == MP_TOKEN_STRING ? MP_PARSE_NODE_STRING : MP_PARSE_NODE_BYTES, qst);
         } else {
@@ -705,7 +705,7 @@ STATIC bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
                     mp_obj_t exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
                         "constant must be an integer");
                     mp_obj_exception_add_traceback(exc, parser->lexer->source_name,
-                        ((mp_parse_node_struct_t*)pn1)->source_line, MP_QSTR_NULL);
+                        ((mp_parse_node_struct_t*)pn1)->source_line, MP_QSTRnull);
                     nlr_raise(exc);
                 }
 
@@ -1138,7 +1138,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
         }
         // add traceback to give info about file name and location
         // we don't have a 'block' name, so just pass the NULL qstr to indicate this
-        mp_obj_exception_add_traceback(exc, lex->source_name, lex->tok_line, MP_QSTR_NULL);
+        mp_obj_exception_add_traceback(exc, lex->source_name, lex->tok_line, MP_QSTRnull);
         nlr_raise(exc);
     }
 
diff --git a/py/parsenum.c b/py/parsenum.c
index ae9b83419..2b01b7259 100644
--- a/py/parsenum.c
+++ b/py/parsenum.c
@@ -41,7 +41,7 @@ STATIC NORETURN void raise_exc(mp_obj_t exc, mp_lexer_t *lex) {
     // exception's type from ValueError to SyntaxError and add traceback info
     if (lex != NULL) {
         ((mp_obj_base_t*)MP_OBJ_TO_PTR(exc))->type = &mp_type_SyntaxError;
-        mp_obj_exception_add_traceback(exc, lex->source_name, lex->tok_line, MP_QSTR_NULL);
+        mp_obj_exception_add_traceback(exc, lex->source_name, lex->tok_line, MP_QSTRnull);
     }
     nlr_raise(exc);
 }
diff --git a/py/qstr.h b/py/qstr.h
index f4375ee0e..8153ef29f 100644
--- a/py/qstr.h
+++ b/py/qstr.h
@@ -35,7 +35,7 @@
 // Note: it would be possible to define MP_QSTR_xxx as qstr_from_str_static("xxx")
 // for qstrs that are referenced this way, but you don't want to have them in ROM.
 
-// first entry in enum will be MP_QSTR_NULL=0, which indicates invalid/no qstr
+// first entry in enum will be MP_QSTRnull=0, which indicates invalid/no qstr
 enum {
 #ifndef NO_QSTR
 #define QDEF(id, str) id,
@@ -61,7 +61,7 @@ typedef struct _qstr_pool_t {
 void qstr_init(void);
 
 mp_uint_t qstr_compute_hash(const byte *data, size_t len);
-qstr qstr_find_strn(const char *str, size_t str_len); // returns MP_QSTR_NULL if not found
+qstr qstr_find_strn(const char *str, size_t str_len); // returns MP_QSTRnull if not found
 
 qstr qstr_from_str(const char *str);
 qstr qstr_from_strn(const char *str, size_t len);
diff --git a/py/repl.c b/py/repl.c
index da0fefb3a..9389b3424 100644
--- a/py/repl.c
+++ b/py/repl.c
@@ -159,7 +159,7 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
         if (str < top) {
             // a complete word, lookup in current object
             qstr q = qstr_find_strn(s_start, s_len);
-            if (q == MP_QSTR_NULL) {
+            if (q == MP_QSTRnull) {
                 // lookup will fail
                 return 0;
             }
diff --git a/tests/unix/extra_coverage.py b/tests/unix/extra_coverage.py
index cb68bae4d..09bb48f0f 100644
--- a/tests/unix/extra_coverage.py
+++ b/tests/unix/extra_coverage.py
@@ -74,3 +74,7 @@ except ZeroDivisionError:
 import uio
 buf = uio.resource_stream('frzstr_pkg2', 'mod.py')
 print(buf.read(21))
+
+# test for MP_QSTR_NULL regression
+from frzqstr import returns_NULL
+print(returns_NULL())
diff --git a/tests/unix/extra_coverage.py.exp b/tests/unix/extra_coverage.py.exp
index 07fde6c09..54c5b63e2 100644
--- a/tests/unix/extra_coverage.py.exp
+++ b/tests/unix/extra_coverage.py.exp
@@ -107,3 +107,4 @@ frzmpy_pkg2.mod
 1
 ZeroDivisionError
 b'# test frozen package'
+NULL
diff --git a/tools/mpy-tool.py b/tools/mpy-tool.py
index 557ee98ff..c6f90e4f8 100755
--- a/tools/mpy-tool.py
+++ b/tools/mpy-tool.py
@@ -70,7 +70,7 @@ class QStrType:
         self.qstr_id = 'MP_QSTR_' + self.qstr_esc
 
 # Initialise global list of qstrs with static qstrs
-global_qstrs = [None] # MP_QSTR_NULL should never be referenced
+global_qstrs = [None] # MP_QSTRnull should never be referenced
 for n in qstrutil.static_qstr_list:
     global_qstrs.append(QStrType(n))