diff --git a/contrib/hstore_plperl/Makefile b/contrib/hstore_plperl/Makefile
index f63cba27456..32ecaa43cbc 100644
--- a/contrib/hstore_plperl/Makefile
+++ b/contrib/hstore_plperl/Makefile
@@ -4,7 +4,6 @@ MODULE_big = hstore_plperl
 OBJS = hstore_plperl.o $(WIN32RES)
 PGFILEDESC = "hstore_plperl - hstore transform for plperl"
 
-PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plperl -I$(top_srcdir)/contrib/hstore
 
 EXTENSION = hstore_plperl hstore_plperlu
 DATA = hstore_plperl--1.0.sql hstore_plperlu--1.0.sql
@@ -13,10 +12,12 @@ REGRESS = hstore_plperl hstore_plperlu create_transform
 EXTRA_INSTALL = contrib/hstore
 
 ifdef USE_PGXS
+PG_CPPFLAGS = -I$(includedir_server)/extension
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
 include $(PGXS)
 else
+PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plperl -I$(top_srcdir)/contrib
 subdir = contrib/hstore_plperl
 top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
diff --git a/contrib/hstore_plperl/hstore_plperl.c b/contrib/hstore_plperl/hstore_plperl.c
index c09bd38d090..61b5557421c 100644
--- a/contrib/hstore_plperl/hstore_plperl.c
+++ b/contrib/hstore_plperl/hstore_plperl.c
@@ -5,7 +5,7 @@
 #include "fmgr.h"
 #include "plperl.h"
 #include "plperl_helpers.h"
-#include "hstore.h"
+#include "hstore/hstore.h"
 
 PG_MODULE_MAGIC;
 
diff --git a/contrib/hstore_plpython/Makefile b/contrib/hstore_plpython/Makefile
index b81735ab910..6877e7a072c 100644
--- a/contrib/hstore_plpython/Makefile
+++ b/contrib/hstore_plpython/Makefile
@@ -4,19 +4,21 @@ MODULE_big = hstore_plpython$(python_majorversion)
 OBJS = hstore_plpython.o $(WIN32RES)
 PGFILEDESC = "hstore_plpython - hstore transform for plpython"
 
-PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpython $(python_includespec) -I$(top_srcdir)/contrib/hstore -DPLPYTHON_LIBNAME='"plpython$(python_majorversion)"'
-
 EXTENSION = hstore_plpythonu hstore_plpython2u hstore_plpython3u
 DATA = hstore_plpythonu--1.0.sql hstore_plpython2u--1.0.sql hstore_plpython3u--1.0.sql
 
 REGRESS = hstore_plpython
 REGRESS_PLPYTHON3_MANGLE := $(REGRESS)
 
+PG_CPPFLAGS = $(python_includespec) -DPLPYTHON_LIBNAME='"plpython$(python_majorversion)"'
+
 ifdef USE_PGXS
+PG_CPPFLAGS += -I$(includedir_server)/extension
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
 include $(PGXS)
 else
+PG_CPPFLAGS += -I$(top_srcdir)/src/pl/plpython -I$(top_srcdir)/contrib
 subdir = contrib/hstore_plpython
 top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
diff --git a/contrib/hstore_plpython/hstore_plpython.c b/contrib/hstore_plpython/hstore_plpython.c
index 218e6612b14..2f24090ff3e 100644
--- a/contrib/hstore_plpython/hstore_plpython.c
+++ b/contrib/hstore_plpython/hstore_plpython.c
@@ -3,7 +3,7 @@
 #include "fmgr.h"
 #include "plpython.h"
 #include "plpy_typeio.h"
-#include "hstore.h"
+#include "hstore/hstore.h"
 
 PG_MODULE_MAGIC;
 
diff --git a/contrib/ltree_plpython/Makefile b/contrib/ltree_plpython/Makefile
index 7e988c79935..ce2c0cd2e2f 100644
--- a/contrib/ltree_plpython/Makefile
+++ b/contrib/ltree_plpython/Makefile
@@ -4,19 +4,21 @@ MODULE_big = ltree_plpython$(python_majorversion)
 OBJS = ltree_plpython.o $(WIN32RES)
 PGFILEDESC = "ltree_plpython - ltree transform for plpython"
 
-PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpython $(python_includespec) -I$(top_srcdir)/contrib/ltree -DPLPYTHON_LIBNAME='"plpython$(python_majorversion)"'
-
 EXTENSION = ltree_plpythonu ltree_plpython2u ltree_plpython3u
 DATA = ltree_plpythonu--1.0.sql ltree_plpython2u--1.0.sql ltree_plpython3u--1.0.sql
 
 REGRESS = ltree_plpython
 REGRESS_PLPYTHON3_MANGLE := $(REGRESS)
 
+PG_CPPFLAGS = $(python_includespec) -DPLPYTHON_LIBNAME='"plpython$(python_majorversion)"'
+
 ifdef USE_PGXS
+PG_CPPFLAGS += -I$(includedir_server)/extension
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
 include $(PGXS)
 else
+PG_CPPFLAGS += -I$(top_srcdir)/src/pl/plpython -I$(top_srcdir)/contrib
 subdir = contrib/ltree_plpython
 top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
diff --git a/contrib/ltree_plpython/ltree_plpython.c b/contrib/ltree_plpython/ltree_plpython.c
index e88636a0a96..b254aa558d1 100644
--- a/contrib/ltree_plpython/ltree_plpython.c
+++ b/contrib/ltree_plpython/ltree_plpython.c
@@ -2,7 +2,7 @@
 
 #include "fmgr.h"
 #include "plpython.h"
-#include "ltree.h"
+#include "ltree/ltree.h"
 
 PG_MODULE_MAGIC;
 
diff --git a/src/pl/plperl/GNUmakefile b/src/pl/plperl/GNUmakefile
index 933abb47c49..39dacf8b2e9 100644
--- a/src/pl/plperl/GNUmakefile
+++ b/src/pl/plperl/GNUmakefile
@@ -100,7 +100,7 @@ uninstall: uninstall-lib uninstall-data
 
 install-data: installdirs
 	$(INSTALL_DATA) $(addprefix $(srcdir)/, $(DATA)) '$(DESTDIR)$(datadir)/extension/'
-	$(INSTALL_DATA) $(srcdir)/plperl.h $(srcdir)/ppport.h '$(DESTDIR)$(includedir_server)'
+	$(INSTALL_DATA) $(srcdir)/plperl.h $(srcdir)/ppport.h $(srcdir)/plperl_helpers.h '$(DESTDIR)$(includedir_server)'
 
 uninstall-data:
 	rm -f $(addprefix '$(DESTDIR)$(datadir)/extension'/, $(notdir $(DATA)))
diff --git a/src/pl/plpython/Makefile b/src/pl/plpython/Makefile
index c17015bbdf5..667a74469ec 100644
--- a/src/pl/plpython/Makefile
+++ b/src/pl/plpython/Makefile
@@ -39,6 +39,21 @@ ifeq ($(python_majorversion),2)
 DATA += plpythonu.control plpythonu--1.0.sql plpythonu--unpackaged--1.0.sql
 endif
 
+# header files to install - it's not clear which of these might be needed
+# so install them all.
+INCS = 	plpython.h \
+	plpy_cursorobject.h \
+	plpy_elog.h \
+	plpy_exec.h \
+	plpy_main.h \
+	plpy_planobject.h \
+	plpy_plpymodule.h \
+	plpy_procedure.h \
+	plpy_resultobject.h \
+	plpy_spi.h \
+	plpy_subxactobject.h \
+	plpy_typeio.h \
+	plpy_util.h
 
 # Python on win32 ships with import libraries only for Microsoft Visual C++,
 # which are not compatible with mingw gcc. Therefore we need to build a
@@ -105,13 +120,14 @@ $(OBJS): | submake-generated-headers
 install: all install-lib install-data
 
 installdirs: installdirs-lib
-	$(MKDIR_P) '$(DESTDIR)$(datadir)/extension' '$(DESTDIR)$(includedir_server)'
+	$(MKDIR_P) '$(DESTDIR)$(datadir)/extension' '$(DESTDIR)$(includedir_server)' '$(DESTDIR)$(pgxsdir)/src/pl/plpython'
 
 uninstall: uninstall-lib uninstall-data
 
 install-data: installdirs
 	$(INSTALL_DATA) $(addprefix $(srcdir)/, $(DATA)) '$(DESTDIR)$(datadir)/extension/'
-	$(INSTALL_DATA) $(srcdir)/plpython.h $(srcdir)/plpy_util.h '$(DESTDIR)$(includedir_server)'
+	$(INSTALL_DATA) $(addprefix $(srcdir)/, $(INCS)) '$(DESTDIR)$(includedir_server)'
+	$(INSTALL_DATA) $(srcdir)/regress-python3-mangle.mk '$(DESTDIR)$(pgxsdir)/src/pl/plpython'
 
 uninstall-data:
 	rm -f $(addprefix '$(DESTDIR)$(datadir)/extension'/, $(notdir $(DATA)))
diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index 9ce03ce684e..6484a67223e 100644
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -506,7 +506,7 @@ sub mkvcbuild
 		my $hstore_plpython = AddTransformModule(
 			'hstore_plpython' . $pymajorver, 'contrib/hstore_plpython',
 			'plpython' . $pymajorver,        'src/pl/plpython',
-			'hstore',                        'contrib/hstore');
+			'hstore',                        'contrib');
 		$hstore_plpython->AddDefine(
 			'PLPYTHON_LIBNAME="plpython' . $pymajorver . '"');
 		my $jsonb_plpython = AddTransformModule(
@@ -517,7 +517,7 @@ sub mkvcbuild
 		my $ltree_plpython = AddTransformModule(
 			'ltree_plpython' . $pymajorver, 'contrib/ltree_plpython',
 			'plpython' . $pymajorver,       'src/pl/plpython',
-			'ltree',                        'contrib/ltree');
+			'ltree',                        'contrib');
 		$ltree_plpython->AddDefine(
 			'PLPYTHON_LIBNAME="plpython' . $pymajorver . '"');
 	}
@@ -753,7 +753,7 @@ sub mkvcbuild
 		my $hstore_plperl = AddTransformModule(
 			'hstore_plperl', 'contrib/hstore_plperl',
 			'plperl',        'src/pl/plperl',
-			'hstore',        'contrib/hstore');
+			'hstore',        'contrib');
 		my $jsonb_plperl = AddTransformModule(
 			'jsonb_plperl', 'contrib/jsonb_plperl',
 			'plperl',       'src/pl/plperl');