--- a/configure.in
+++ b/configure.in
@@ -6,6 +6,7 @@
 dnl NOTE: configure.in requires autoconf 2.57 or more recent.
 
 AC_INIT(ngrep.c)
+AC_CONFIG_SUBDIRS([regex-0.12])
 
 AC_MSG_RESULT
 AC_MSG_RESULT(Configuring System ...)
--- a/regex-0.12/Makefile.in
+++ b/regex-0.12/Makefile.in
@@ -26,13 +26,13 @@
 #   -DEXTRACT_MACROS to use the macros EXTRACT_* (as opposed to
 #           the corresponding C procedures).  If not -DDEBUG, the macros
 #           are used.
-CPPFLAGS = 
+CPPFLAGS ?= 
 
 # Likewise, you can override CFLAGS to optimize, use -Wall, etc.
-CFLAGS = -g
+CFLAGS ?= -g
 
 # Ditto for LDFLAGS and LOADLIBES.
-LDFLAGS =
+LDFLAGS ?=
 LOADLIBES =
 
 srcdir = @srcdir@