diff --git a/t/porting/cpphdrcheck.t b/t/porting/cpphdrcheck.t
index 4f98f56ff686..a07b2df5a1c5 100644
--- a/t/porting/cpphdrcheck.t
+++ b/t/porting/cpphdrcheck.t
@@ -47,7 +47,10 @@ my $ccflags = $Config{ccflags};
 # we add a similar C++ -std
 $ccflags  =~ s/-std[:=]\S+//;
 
-$ccflags = "-I" . File::Spec->catdir($cwd, "..");
+$ccflags = join " ", map { "-I$_" }
+  File::Spec->catdir($cwd, ".."),
+  # win32 has special config.h handling during the build
+  File::Spec->catdir($cwd, "..", "lib", "CORE");
 
 for my $std (sort keys $ccpp_cfg->{stdargs}->%*) {
     my $code = get_source("cpp$std");