diff --git a/configure.ac b/configure.ac
index 3d1f88a..cca9602 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5,10 +5,10 @@ AC_CONFIG_MACRO_DIRS([m4])
 AM_INIT_AUTOMAKE([foreign -Wall -Werror subdir-objects])
 AC_PROG_CC
 if test "x$ac_cv_env_CFLAGS_set" != "xset"; then
-  CFLAGS="-O2"
+  CFLAGS=""
 fi
 
-STRICT_CFLAGS="-Wall -Wextra -Werror -pipe -Wpedantic -Wconversion -Wshadow"
+STRICT_CFLAGS="-Wall -Wextra -Werror -pipe -Wpedantic -Wconversion -Wshadow -Wvla"
 AC_SUBST([STRICT_CFLAGS])
 
 AM_PROG_AR
@@ -35,6 +35,22 @@ AS_IF([test "x$enable_tests" = "xyes"], [
 	])
 ])
 
+# --enable-debug
+AC_ARG_ENABLE(
+			  [debug],
+			  [AS_HELP_STRING([--enable-debug], [Enable debug build: -g -O0 (default: no)])],
+			  [enable_debug=$enableval],
+			  [enable_debug=no]
+			  )
+AM_CONDITIONAL([ENABLE_DEBUG], [test "x$enable_debug" = "xyes"])
+
+AS_IF([test "x$enable_debug" = "xyes"],
+	  [CFLAGS="-g -O0"],
+	  [CFLAGS="-O2"],
+	  )
+
+AC_SUBST([DEBUG_CFLAGS])
+
 AC_CONFIG_FILES([
 	Makefile
 	src/Makefile
@@ -50,7 +66,7 @@ AC_MSG_NOTICE([
   ---------------
   prefix : $prefix
   CC     : $CC
-  CFLAGS : $STRICT_CFLAGS
+  CFLAGS : $STRICT_CFLAGS $CFLAGS
   tests  : $enable_tests
 ])