diff --git a/configure b/configure
index d78992c1ed7..542bf7355fd 100755
--- a/configure
+++ b/configure
@@ -671,7 +671,7 @@ python_majorversion
 PYTHON
 perl_embed_ldflags
 perl_embed_ccflags
-perl_includedir
+perl_includespec
 perl_useshrplib
 perl_privlibexp
 perl_archlibexp
@@ -7540,11 +7540,12 @@ documentation for details.  Use --without-perl to disable building
 PL/Perl." "$LINENO" 5
   fi
   # On most platforms, archlibexp is also where the Perl include files live ...
-  perl_includedir="$perl_archlibexp"
-  # ... but on some macOS versions, we must look under $PG_SYSROOT instead
-  if test x"$PG_SYSROOT" != x"" ; then
+  perl_includespec="-I$perl_archlibexp/CORE"
+  # ... but on newer macOS versions, we must use -iwithsysroot to look
+  # under $PG_SYSROOT
+  if test \! -f "$perl_archlibexp/CORE/perl.h" ; then
     if test -f "$PG_SYSROOT$perl_archlibexp/CORE/perl.h" ; then
-      perl_includedir="$PG_SYSROOT$perl_archlibexp"
+      perl_includespec="-iwithsysroot $perl_archlibexp/CORE"
     fi
   fi
 
@@ -15183,11 +15184,6 @@ eval TCL_SHARED_BUILD=\"$TCL_SHARED_BUILD\"
       as_fn_error $? "cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl." "$LINENO" 5
     fi
-    # Some macOS versions report an include spec that uses -iwithsysroot.
-    # We don't really want to use -isysroot, so translate that if we can.
-    if test x"$PG_SYSROOT" != x"" ; then
-        TCL_INCLUDE_SPEC="`echo "$TCL_INCLUDE_SPEC" | sed "s|-iwithsysroot */|-I $PG_SYSROOT/|"`"
-    fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
     CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
@@ -15205,7 +15201,7 @@ fi
 # check for <perl.h>
 if test "$with_perl" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$CPPFLAGS -I$perl_includedir/CORE"
+  CPPFLAGS="$CPPFLAGS $perl_includespec"
   ac_fn_c_check_header_compile "$LINENO" "perl.h" "ac_cv_header_perl_h" "#include <EXTERN.h>
 "
 if test "x$ac_cv_header_perl_h" = xyes; then :
diff --git a/configure.in b/configure.in
index ec2a93f94bb..44e345666ae 100644
--- a/configure.in
+++ b/configure.in
@@ -927,14 +927,15 @@ documentation for details.  Use --without-perl to disable building
 PL/Perl.])
   fi
   # On most platforms, archlibexp is also where the Perl include files live ...
-  perl_includedir="$perl_archlibexp"
-  # ... but on some macOS versions, we must look under $PG_SYSROOT instead
-  if test x"$PG_SYSROOT" != x"" ; then
+  perl_includespec="-I$perl_archlibexp/CORE"
+  # ... but on newer macOS versions, we must use -iwithsysroot to look
+  # under $PG_SYSROOT
+  if test \! -f "$perl_archlibexp/CORE/perl.h" ; then
     if test -f "$PG_SYSROOT$perl_archlibexp/CORE/perl.h" ; then
-      perl_includedir="$PG_SYSROOT$perl_archlibexp"
+      perl_includespec="-iwithsysroot $perl_archlibexp/CORE"
     fi
   fi
-  AC_SUBST(perl_includedir)dnl
+  AC_SUBST(perl_includespec)dnl
   PGAC_CHECK_PERL_EMBED_CCFLAGS
   PGAC_CHECK_PERL_EMBED_LDFLAGS
 fi
@@ -2040,11 +2041,6 @@ if test "$with_tcl" = yes; then
       AC_MSG_ERROR([cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl.])
     fi
-    # Some macOS versions report an include spec that uses -iwithsysroot.
-    # We don't really want to use -isysroot, so translate that if we can.
-    if test x"$PG_SYSROOT" != x"" ; then
-        TCL_INCLUDE_SPEC="`echo "$TCL_INCLUDE_SPEC" | sed "s|-iwithsysroot */|-I $PG_SYSROOT/|"`"
-    fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
     CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
@@ -2055,7 +2051,7 @@ fi
 # check for <perl.h>
 if test "$with_perl" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$CPPFLAGS -I$perl_includedir/CORE"
+  CPPFLAGS="$CPPFLAGS $perl_includespec"
   AC_CHECK_HEADER(perl.h, [], [AC_MSG_ERROR([header file <perl.h> is required for Perl])],
                   [#include <EXTERN.h>])
   # While we're at it, check that we can link to libperl.
diff --git a/contrib/hstore_plperl/Makefile b/contrib/hstore_plperl/Makefile
index d37e99b1f44..32d7c320c60 100644
--- a/contrib/hstore_plperl/Makefile
+++ b/contrib/hstore_plperl/Makefile
@@ -41,8 +41,5 @@ SHLIB_LINK_INTERNAL += -L../hstore -l hstore
 SHLIB_LINK += $(perl_embed_ldflags)
 endif
 
-# As with plperl we need to make sure that the CORE directory is included
-# last, probably because it sometimes contains some header files with names
-# that clash with some of ours, or with some that we include, notably on
-# Windows.
-override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) -I$(perl_includedir)/CORE
+# As with plperl we need to include the perl_includespec directory last.
+override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index f76beee9b44..5d6a2ceaa92 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -306,7 +306,7 @@ else
 endif
 perl_archlibexp		= @perl_archlibexp@
 perl_privlibexp		= @perl_privlibexp@
-perl_includedir		= @perl_includedir@
+perl_includespec	= @perl_includespec@
 perl_embed_ccflags	= @perl_embed_ccflags@
 perl_embed_ldflags	= @perl_embed_ldflags@
 
diff --git a/src/pl/plperl/GNUmakefile b/src/pl/plperl/GNUmakefile
index d1c84279a6a..0846e60cd81 100644
--- a/src/pl/plperl/GNUmakefile
+++ b/src/pl/plperl/GNUmakefile
@@ -12,12 +12,13 @@ override CPPFLAGS += -DPLPERL_HAVE_UID_GID
 override CPPFLAGS += -Wno-comment
 endif
 
-# Note: we need to make sure that the CORE directory is included last,
+# Note: we need to include the perl_includespec directory last,
 # probably because it sometimes contains some header files with names
 # that clash with some of ours, or with some that we include, notably on
 # Windows.
-override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(perl_embed_ccflags) -I$(perl_includedir)/CORE
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)
 
+# this is often, but not always, the same directory named by perl_includespec
 rpathdir = $(perl_archlibexp)/CORE
 
 PGFILEDESC = "PL/Perl - procedural language"
diff --git a/src/template/darwin b/src/template/darwin
index 70227335669..159d8bb1275 100644
--- a/src/template/darwin
+++ b/src/template/darwin
@@ -3,9 +3,8 @@
 # Note: Darwin is the original code name for macOS, also known as OS X.
 # We still use "darwin" as the port name, partly because config.guess does.
 
-# Select where some include files should be sought.
-# We may eventually be forced to use "-isysroot" with this value,
-# but for now, it only affects Perl and Tcl include files.
+# Some configure tests require explicit knowledge of where the Xcode "sysroot"
+# is.  We try to avoid having this leak into configure's results, though.
 if test x"$PG_SYSROOT" = x"" ; then
   PG_SYSROOT=`xcodebuild -version -sdk macosx Path 2>/dev/null`
 fi