diff --git a/site_scons/site_tools/micropython/qstrdefs.py b/site_scons/site_tools/micropython/qstrdefs.py
index 9563067d42..5e4e1f2bb2 100644
--- a/site_scons/site_tools/micropython/qstrdefs.py
+++ b/site_scons/site_tools/micropython/qstrdefs.py
@@ -5,8 +5,9 @@ QSTR_BLACKLIST = set(['NULL', 'number_of'])
 
 
 def process(source, target):
+    re_qstr = re.compile(r'MP_QSTR_[_a-zA-Z0-9]+')
     for line in source:
-        for match in re.findall(r'MP_QSTR_[_a-zA-Z0-9]+', line):
+        for match in re_qstr.findall(line):
             name = match.replace('MP_QSTR_', '')
             if name not in QSTR_BLACKLIST:
                 target.write('Q(%s)\n' % name)