diff --git a/xkeymap.c b/xkeymap.c
index 1fcb5f7..7a23854 100644
--- a/xkeymap.c
+++ b/xkeymap.c
@@ -20,7 +20,7 @@
 
 #include <X11/Xlib.h>
 #define XK_MISCELLANY
-#include <X11/keysymdef.h>
+#include <X11/keysym.h>
 #include <ctype.h>
 #include <limits.h>
 #include <time.h>
@@ -34,6 +34,7 @@
 extern Display *display;
 extern char keymapname[16];
 extern int keylayout;
+extern int win_button_size;
 extern BOOL enable_compose;
 
 static BOOL keymap_loaded;
@@ -307,6 +308,13 @@ handle_special_keys(uint32 keysym, unsigned int state, uint32 ev_time, BOOL pres
 				rdp_send_scancode(ev_time, RDP_KEYRELEASE, SCANCODE_CHAR_LCTRL);
 			}
 			return True;
+
+		case XK_space:
+			/* Prevent access to the Windows system menu in single app mode */
+			if (win_button_size
+			    && (get_key_state(state, XK_Alt_L) || get_key_state(state, XK_Alt_R)))
+				return True;
+
 	}
 	return False;
 }
diff --git a/xwin.c b/xwin.c
index 58003a6..8b0d2bc 100644
--- a/xwin.c
+++ b/xwin.c
@@ -858,9 +858,14 @@ xwin_process_events(void)
 				/* If win_button_size is nonzero, enable single app mode */
 				if (xevent.xbutton.y < win_button_size)
 				{
-					if (xevent.xbutton.x >= width - win_button_size)
+					if (xevent.xbutton.x < win_button_size)
 					{
-						/* The close button, do nothing */
+						/* The system menu, do not send to server */
+						break;
+					}
+					else if (xevent.xbutton.x >= width - win_button_size)
+					{
+						/* The close button, continue */
 						;
 					}
 					else if (xevent.xbutton.x >= width - win_button_size * 2)