diff --git a/py/py.mk b/py/py.mk
index 01a8026744..c4e2a79e66 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -282,6 +282,10 @@ $(HEADER_BUILD)/qstrdefs.generated.h: $(PY_QSTR_DEFS) $(QSTR_DEFS) $(QSTR_DEFS_C
 	$(Q)cat $(PY_QSTR_DEFS) $(QSTR_DEFS) $(QSTR_DEFS_COLLECTED) | $(SED) 's/^Q(.*)/"&"/' | $(CPP) $(CFLAGS) - | $(SED) 's/^"\(Q(.*)\)"/\1/' > $(HEADER_BUILD)/qstrdefs.preprocessed.h
 	$(Q)$(PYTHON) $(PY_SRC)/makeqstrdata.py $(HEADER_BUILD)/qstrdefs.preprocessed.h > $@
 
+# Force nlr code to always be compiled with space-saving optimisation so
+# that the function preludes are of a minimal and predictable form.
+$(PY_BUILD)/nlr%.o: CFLAGS += -Os
+
 # emitters
 
 $(PY_BUILD)/emitnx64.o: CFLAGS += -DN_X64