diff --git a/src/backend/utils/adt/Makefile b/src/backend/utils/adt/Makefile
index 279ff15ade..41b486bcef 100644
--- a/src/backend/utils/adt/Makefile
+++ b/src/backend/utils/adt/Makefile
@@ -8,6 +8,8 @@ subdir = src/backend/utils/adt
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
+
 # keep this list arranged alphabetically or it gets to be a mess
 OBJS = \
 	acl.o \
diff --git a/src/test/isolation/Makefile b/src/test/isolation/Makefile
index edff04f041..0d452c89d4 100644
--- a/src/test/isolation/Makefile
+++ b/src/test/isolation/Makefile
@@ -9,7 +9,8 @@ subdir = src/test/isolation
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-override CPPFLAGS := -I$(srcdir) -I$(libpq_srcdir) -I$(srcdir)/../regress $(CPPFLAGS)
+override CPPFLAGS := -I. -I$(srcdir) -I$(libpq_srcdir) \
+	-I$(srcdir)/../regress $(CPPFLAGS)
 
 OBJS = \
 	$(WIN32RES) \