diff --git a/js/src/config/rules.mk b/js/src/config/rules.mk
index 2b8d875df50..ae8fbae876c 100644
--- a/js/src/config/rules.mk
+++ b/js/src/config/rules.mk
@@ -1540,7 +1540,7 @@ $(XPIDL_GEN_DIR)/%.h: %.idl $(XPIDL_DEPS) $(XPIDL_GEN_DIR)/.done
 	$(PYTHON) $(topsrcdir)/config/pythonpath.py \
 	  -I$(topsrcdir)/other-licenses/ply \
 	  -I$(topsrcdir)/xpcom/idl-parser \
-	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(DEPTH)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
+	  $(topsrcdir)/xpcom/idl-parser/header.py --cachedir=$(topsrcdir)/xpcom/idl-parser $(XPIDL_FLAGS) $(_VPATH_SRCS) -d $(MDDEPDIR)/$(@F).pp -o $@
 	@if test -n "$(findstring $*.h, $(EXPORTS))"; \
 	  then echo "*** WARNING: file $*.h generated from $*.idl overrides $(srcdir)/$*.h"; else true; fi