diff --git a/src/tools/pg_bsd_indent/Makefile b/src/tools/pg_bsd_indent/Makefile
index b138bb8b12e..d176ceb326e 100644
--- a/src/tools/pg_bsd_indent/Makefile
+++ b/src/tools/pg_bsd_indent/Makefile
@@ -13,6 +13,8 @@ subdir = src/tools/pg_bsd_indent
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
+override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
+
 OBJS = \
 	$(WIN32RES) \
 	args.o \