--- odt2txt-0.5/Makefile.cflags	2014-11-18 18:10:08.000000000 +0100
+++ odt2txt-0.5/Makefile	2017-09-17 00:47:39.581408145 +0200
@@ -3,11 +3,11 @@
 UNAME_O := $(shell uname -o 2>/dev/null || echo unknown)
 
 ifdef DEBUG
-CFLAGS = -O0 -g -Wextra -DMEMDEBUG -DSTRBUF_CHECK
+CFLAGS += -O0 -g -Wextra -DMEMDEBUG -DSTRBUF_CHECK
 #LDFLAGS = -lefence
 LDFLAGS += -g
 else
-CFLAGS = -O2
+CFLAGS += -O2
 endif
 
 ifdef NO_ICONV