--- a/config/rules.mk
+++ b/config/rules.mk
@@ -1025,16 +1025,17 @@ define PREPROCESS_RULES
 _PREPROCESSED_$1_FILES := $$(call _group_srcs,$1,$$($2))
 # Make preprocessed files PHONY so they are always executed, since they are
 # manual targets and we don't necessarily write to $@.
 .PHONY: $$(_PREPROCESSED_$1_FILES)
 
 # Hack up VPATH so we can reach the sources. Eg: 'make Parser.i' may need to
 # reach $(srcdir)/frontend/Parser.i
 vpath %.$1 $$(addprefix $$(srcdir)/,$$(sort $$(dir $$($2))))
+vpath %.$1 $$(addprefix $$(CURDIR)/,$$(sort $$(dir $$($2))))
 
 $$(_PREPROCESSED_$1_FILES): _DEPEND_CFLAGS=
 $$(_PREPROCESSED_$1_FILES): %.i: %.$1
 	$$(REPORT_BUILD_VERBOSE)
 	$$(addprefix $$(MKDIR) -p ,$$(filter-out .,$$(@D)))
 	$$($3) -C $$(PREPROCESS_OPTION)$$@ $(foreach var,$4,$$($(var))) $$($$(notdir $$<)_FLAGS) $$(_VPATH_SRCS)
 
 endef