--- config.def.h
+++ config.def.h
@@ -9,6 +9,7 @@ static const char selbordercolor[]  = "#005577";
 static const char selbgcolor[]      = "#005577";
 static const char selfgcolor[]      = "#eeeeee";
 static const unsigned int borderpx  = 1;        /* border pixel of windows */
+static const unsigned int gappx     = 1;        /* gap pixel between windows */
 static const unsigned int snap      = 32;       /* snap pixel */
 static const Bool showbar           = True;     /* False means no bar */
 static const Bool topbar            = True;     /* False means bottom bar */
