--- a/CPP/7zip/7zip_gcc.mak
+++ b/CPP/7zip/7zip_gcc.mak
@@ -24,7 +24,7 @@ PROGPATH_STATIC = $(O)/$(PROG)s
 
 
 ifneq ($(CC), xlc)
-CFLAGS_WARN_WALL = -Werror -Wall -Wextra
+CFLAGS_WARN_WALL = -Wall -Wextra
 endif
 
 # for object file
@@ -50,7 +50,7 @@ endif
 endif
 
 # CFLAGS_BASE_LIST = -S
-CFLAGS_BASE = -O2 $(CFLAGS_BASE_LIST) $(CFLAGS_WARN_WALL) $(CFLAGS_WARN) \
+CFLAGS_BASE = $(CFLAGS_BASE_LIST) $(CFLAGS_WARN_WALL) $(CFLAGS_WARN) -D_GNU_SOURCE \
  $(CFLAGS_DEBUG) -D_REENTRANT -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE \
  -fPIC