diff --git a/ports/esp32s2/Makefile b/ports/esp32s2/Makefile
index a97ab0b00f..8d891edd02 100644
--- a/ports/esp32s2/Makefile
+++ b/ports/esp32s2/Makefile
@@ -269,7 +269,7 @@ menuconfig: $(BUILD)/esp-idf/config
 	$(Q)grep -Fvxf $(DEBUG_SDKCONFIG) -f $(FLASH_SDKCONFIG) $(BUILD)/sdkconfig.diff > boards/$(BOARD)/sdkconfig
 
 # qstr builds include headers so we need to make sure they are up to date
-$(HEADER_BUILD)/qstr.i.last: | $(BUILD)/esp-idf/config/sdkconfig.h
+$(HEADER_BUILD)/qstr.split: | $(BUILD)/esp-idf/config/sdkconfig.h
 
 ESP_IDF_COMPONENTS_LINK = freertos log hal esp_system esp_adc_cal esp32s2 bootloader_support pthread esp_timer vfs spi_flash app_update esp_common esp32s2 heap newlib driver xtensa soc esp_ringbuf esp_wifi esp_event wpa_supplicant mbedtls efuse nvs_flash esp_netif lwip esp_rom esp-tls
 
diff --git a/py/genlast.py b/py/genlast.py
new file mode 100644
index 0000000000..1df2a24825
--- /dev/null
+++ b/py/genlast.py
@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+
+import sys
+import re
+import os
+import itertools
+from concurrent.futures import ProcessPoolExecutor
+import multiprocessing
+import threading
+import subprocess
+
+from makeqstrdefs import qstr_unescape, QSTRING_BLACK_LIST
+
+re_line = re.compile(r"#[line]*\s(\d+)\s\"([^\"]+)\"", re.DOTALL)
+re_qstr = re.compile(r'MP_QSTR_[_a-zA-Z0-9]+', re.DOTALL)
+re_translate = re.compile(r'translate\(\"((?:(?=(\\?))\2.)*?)\"\)', re.DOTALL)
+
+def write_out(fname, output_dir, output):
+    if output:
+        for m, r in [("/", "__"), ("\\", "__"), (":", "@"), ("..", "@@")]:
+            fname = fname.replace(m, r)
+        with open(output_dir + "/" + fname + ".qstr", "w") as f:
+            f.write("\n".join(output) + "\n")
+
+def process_file(fname, output_dir, content):
+    content = content.decode('utf-8', errors='ignore')
+    output = []
+    for match in re_qstr.findall(content):
+        name = match.replace('MP_QSTR_', '')
+        if name not in QSTRING_BLACK_LIST:
+            output.append('Q(' + qstr_unescape(name) + ')')
+    for match in re_translate.findall(content):
+        output.append('TRANSLATE("' + match[0] + '")')
+
+    write_out(fname, output_dir, output)
+
+
+def checkoutput1(args):
+    info = subprocess.run(args, check=True, stdout=subprocess.PIPE, input='')
+    return info.stdout
+
+def preprocess(command, output_dir, fn):
+    try:
+        output = checkoutput1(command + [fn])
+        process_file(fn, output_dir, output)
+    except Exception as e:
+        print(e, file=sys.stderr)
+
+def maybe_preprocess(command, output_dir, fn):
+    if subprocess.call(["grep", "-lqE", "(MP_QSTR|translate)", fn]) == 0:
+        preprocess(command, output_dir, fn)
+
+if __name__ == '__main__':
+
+
+    idx1 = sys.argv.index('--')
+    idx2 = sys.argv.index('--', idx1+1)
+    output_dir = sys.argv[1]
+    check = sys.argv[2:idx1]
+    always = sys.argv[idx1+1:idx2]
+    command = sys.argv[idx2+1:]
+
+    if not os.path.isdir(output_dir):
+        os.makedirs(output_dir)
+
+    # Mac and Windows use 'spawn'.  Uncomment this during testing to catch spawn-specific problems on Linux.
+    #multiprocessing.set_start_method("spawn")
+    executor = ProcessPoolExecutor(max_workers=multiprocessing.cpu_count() + 1)
+    executor.map(maybe_preprocess, itertools.repeat(command), itertools.repeat(output_dir), check)
+    executor.map(preprocess, itertools.repeat(command), itertools.repeat(output_dir), always)
+    executor.shutdown()
diff --git a/py/mkrules.mk b/py/mkrules.mk
index 0b3ecc0e17..549b0e5e42 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -76,18 +76,14 @@ $(OBJ): | $(HEADER_BUILD)/qstrdefs.enum.h $(HEADER_BUILD)/mpversion.h
 # - if anything in QSTR_GLOBAL_DEPENDENCIES is newer, then process all source files ($^)
 # - else, if list of newer prerequisites ($?) is not empty, then process just these ($?)
 # - else, process all source files ($^) [this covers "make -B" which can set $? to empty]
-$(HEADER_BUILD)/qstr.i.last: $(SRC_QSTR) $(SRC_QSTR_PREPROCESSOR) $(QSTR_GLOBAL_DEPENDENCIES) | $(HEADER_BUILD)/mpversion.h
+$(HEADER_BUILD)/qstr.split: $(SRC_QSTR) $(SRC_QSTR_PREPROCESSOR) $(QSTR_GLOBAL_DEPENDENCIES) | $(HEADER_BUILD)/mpversion.h $(PY_SRC)/genlast.py
 	$(STEPECHO) "GEN $@"
-	$(Q)grep -lE "(MP_QSTR|translate)" $(if $(filter $?,$(QSTR_GLOBAL_DEPENDENCIES)),$^,$(if $?,$?,$^)) | xargs $(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS) $(SRC_QSTR_PREPROCESSOR) >$(HEADER_BUILD)/qstr.i.last;
-
-$(HEADER_BUILD)/qstr.split: $(HEADER_BUILD)/qstr.i.last $(PY_SRC)/makeqstrdefs.py
-	$(STEPECHO) "GEN $@"
-	$(Q)$(PYTHON3) $(PY_SRC)/makeqstrdefs.py split $(HEADER_BUILD)/qstr.i.last $(HEADER_BUILD)/qstr $(QSTR_DEFS_COLLECTED)
+	$(Q)$(PYTHON3) $(PY_SRC)/genlast.py $(HEADER_BUILD)/qstr $(if $(filter $?,$(QSTR_GLOBAL_DEPENDENCIES)),$^,$(if $?,$?,$^)) --  $(SRC_QSTR_PREPROCESSOR) -- $(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS)
 	$(Q)touch $@
 
 $(QSTR_DEFS_COLLECTED): $(HEADER_BUILD)/qstr.split $(PY_SRC)/makeqstrdefs.py
 	$(STEPECHO) "GEN $@"
-	$(Q)$(PYTHON3) $(PY_SRC)/makeqstrdefs.py cat $(HEADER_BUILD)/qstr.i.last $(HEADER_BUILD)/qstr $(QSTR_DEFS_COLLECTED)
+	$(Q)$(PYTHON3) $(PY_SRC)/makeqstrdefs.py cat - $(HEADER_BUILD)/qstr $(QSTR_DEFS_COLLECTED)
 
 # $(sort $(var)) removes duplicates
 #