diff --git a/config.def.h b/config.def.h
index 3d37dca..d7c11a1 100644
--- a/config.def.h
+++ b/config.def.h
@@ -8,6 +8,9 @@ static const char *colorname[NUMCOLS] = {
 	[FAILED] = "#CC3333",   /* wrong password */
 };
 
+/* lock screen opacity */
+static const float alpha = 1;
+
 /* treat a cleared input like a wrong password (color) */
 static const int failonclear = 1;
 
diff --git a/config.h b/config.h
index 234315f..a25075d 100644
--- a/config.h
+++ b/config.h
@@ -8,6 +8,9 @@ static const char *colorname[NUMCOLS] = {
 	[FAILED] = "#FF5555",   /* wrong password */
 };
 
+/* lock screen opacity */
+static const float alpha = 1;
+
 /* treat a cleared input like a wrong password (color) */
 static const int failonclear = 1;
 
diff --git a/slock.c b/slock.c
index 968fbf1..4b8e12e 100644
--- a/slock.c
+++ b/slock.c
@@ -18,6 +18,7 @@
 #include <X11/keysym.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
+#include <X11/Xatom.h>
 
 #include "arg.h"
 #include "util.h"
@@ -334,6 +335,9 @@ lockscreen(Display *dpy, struct xrandr *rr, int screen)
 				XRRSelectInput(dpy, lock->win, RRScreenChangeNotifyMask);
 
 			XSelectInput(dpy, lock->root, SubstructureNotifyMask);
+            unsigned int opacity = (unsigned int)(alpha * 0xffffffff);
+            XChangeProperty(dpy, lock->win, XInternAtom(dpy, "_NET_WM_WINDOW_OPACITY", False), XA_CARDINAL, 32, PropModeReplace, (unsigned char *)&opacity, 1L);
+            XSync(dpy, False);
 			return lock;
 		}