diff -ru ed-1.17.orig/configure ed-1.17/configure
--- ed-1.17.orig/configure	2021-01-06 14:06:29.000000000 +0100
+++ ed-1.17/configure	2021-01-13 12:29:03.995851327 +0100
@@ -23,7 +23,7 @@
 program_prefix=
 CC=gcc
 CPPFLAGS=
-CFLAGS='-Wall -W -O2'
+CFLAGS ?= '-Wall -W -O2'
 LDFLAGS=
 
 # checking whether we are using GNU C.