diff --git a/esp8266/Makefile b/esp8266/Makefile
index e13082e18..26b5e8626 100644
--- a/esp8266/Makefile
+++ b/esp8266/Makefile
@@ -171,9 +171,7 @@ endif
 
 $(BUILD)/uart.o: $(CONFVARS_FILE)
 
-$(BUILD)/frozen.c: $(wildcard $(FROZEN_DIR)/*) $(CONFVARS_FILE)
-	$(ECHO) "Generating $@"
-	$(Q)$(MAKE_FROZEN) $(FROZEN_DIR) > $@
+FROZEN_EXTRA_DEPS = $(CONFVARS_FILE)
 
 # to build .mpy files from .py files
 $(BUILD)/$(FROZEN_MPY_DIR)/%.mpy: $(FROZEN_MPY_DIR)/%.py
diff --git a/py/mkenv.mk b/py/mkenv.mk
index b7f8c2aff..e7262907c 100644
--- a/py/mkenv.mk
+++ b/py/mkenv.mk
@@ -58,6 +58,8 @@ CXX += -m32
 LD += -m32
 endif
 
+MAKE_FROZEN = ../tools/make-frozen.py
+
 all:
 .PHONY: all
 
diff --git a/py/mkrules.mk b/py/mkrules.mk
index a3a408dc8..26e4aeab3 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -100,6 +100,12 @@ $(OBJ_DIRS):
 $(HEADER_BUILD):
 	$(MKDIR) -p $@
 
+ifneq ($(FROZEN_DIR),)
+$(BUILD)/frozen.c: $(wildcard $(FROZEN_DIR)/*) $(HEADER_BUILD) $(FROZEN_EXTRA_DEPS)
+	$(ECHO) "Generating $@"
+	$(Q)$(MAKE_FROZEN) $(FROZEN_DIR) > $@
+endif
+
 ifneq ($(PROG),)
 # Build a standalone executable (unix does this)