Index: Makefile
--- Makefile.orig	2019-02-04 00:04:37.000000000 +0100
+++ Makefile	2019-02-17 15:37:28.378411000 +0100
@@ -53,8 +53,8 @@
 
 # Headers for other extensions to build against
 install-headers:
-	$(MKDIR_P) $(headers_dir)
-	$(INSTALL_DATA) $(CURDIR)/include/*.h '$(headers_dir)'
+	$(MKDIR_P) $(DESTDIR)$(headers_dir)
+	$(INSTALL_DATA) $(CURDIR)/include/*.h $(DESTDIR)$(headers_dir)
 
 install: install-headers