diff -rupN mingw-w64-v6.0.0/mingw-w64-tools/widl/Makefile.am mingw-w64-v6.0.0-new/mingw-w64-tools/widl/Makefile.am
--- mingw-w64-v6.0.0/mingw-w64-tools/widl/Makefile.am	2018-09-14 16:16:43.000000000 +0200
+++ mingw-w64-v6.0.0-new/mingw-w64-tools/widl/Makefile.am	2019-05-07 17:55:56.298194052 +0200
@@ -58,7 +58,7 @@ widl_SOURCES = src/widl.h \
   include/pathtools.h \
   include/winnt.rh
 
-widl_CPPFLAGS = -I$(top_srcdir)/include -DDEFAULT_INCLUDE_DIR=\"$(includedir)/../$(target)/include\" -DDEFAULT_BINDIR=\"$(bindir)\"
+widl_CPPFLAGS = -I$(top_srcdir)/include -DDEFAULT_INCLUDE_DIR=\"$(prefix)/$(target)/sys-root/mingw/include\" -DDEFAULT_BINDIR=\"$(bindir)\"
 widl_CFLAGS = -O3 -g -Wall -Wformat -Wpacked -Wmissing-declarations -Wimplicit-function-declaration -Wmissing-prototypes -Wstrict-aliasing=2
 
 DISTCHECK_CONFIGURE_FLAGS = --host=$(host) --target=$(target)
diff -rupN mingw-w64-v6.0.0/mingw-w64-tools/widl/Makefile.in mingw-w64-v6.0.0-new/mingw-w64-tools/widl/Makefile.in
--- mingw-w64-v6.0.0/mingw-w64-tools/widl/Makefile.in	2018-09-14 16:16:43.000000000 +0200
+++ mingw-w64-v6.0.0-new/mingw-w64-tools/widl/Makefile.in	2019-05-07 17:55:56.299194042 +0200
@@ -368,7 +368,7 @@ widl_SOURCES = src/widl.h \
   include/pathtools.h \
   include/winnt.rh
 
-widl_CPPFLAGS = -I$(top_srcdir)/include -DDEFAULT_INCLUDE_DIR=\"$(includedir)/../$(target)/include\" -DDEFAULT_BINDIR=\"$(bindir)\"
+widl_CPPFLAGS = -I$(top_srcdir)/include -DDEFAULT_INCLUDE_DIR=\"$(prefix)/$(target)/sys-root/mingw/include\" -DDEFAULT_BINDIR=\"$(bindir)\"
 widl_CFLAGS = -O3 -g -Wall -Wformat -Wpacked -Wmissing-declarations -Wimplicit-function-declaration -Wmissing-prototypes -Wstrict-aliasing=2
 DISTCHECK_CONFIGURE_FLAGS = --host=$(host) --target=$(target)
 all: all-am