diff --git a/py/py.mk b/py/py.mk
index e064b325e5..ae12e1976d 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -106,9 +106,8 @@ $(BUILD)/extmod/modbtree.o: CFLAGS += $(BTREE_DEFS)
 endif
 
 ifeq ($(CIRCUITPY_ULAB),1)
-SRC_MOD += $(patsubst $(TOP)/%,%,$(wildcard $(TOP)/extmod/ulab/code/*.c))
-SRC_MOD += $(patsubst $(TOP)/%,%,$(wildcard $(TOP)/extmod/ulab/code/*/*.c))
-SRC_MOD += $(patsubst $(TOP)/%,%,$(wildcard $(TOP)/extmod/ulab/code/*/*/*.c))
+ULAB_SRCS := $(shell find $(TOP)/extmod/ulab/code -type f -name "*.c")
+SRC_MOD += $(patsubst $(TOP)/%,%,$(ULAB_SRCS))
 CFLAGS_MOD += -DCIRCUITPY_ULAB=1 -DMODULE_ULAB_ENABLED=1 -iquote $(TOP)/extmod/ulab/code
 $(BUILD)/extmod/ulab/code/%.o: CFLAGS += -Wno-missing-declarations -Wno-missing-prototypes -Wno-unused-parameter -Wno-float-equal -Wno-sign-compare -Wno-cast-align -Wno-shadow -DCIRCUITPY
 endif