diff --git a/CMakeLists.txt b/CMakeLists.txt
index b879331..7f95454 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -30,7 +30,7 @@ OPTION(MAIKO_DISPLAY_X11 "Use X11 for display." ON)
 IF(MAIKO_DISPLAY_X11)
   FIND_PACKAGE(X11 REQUIRED)
   SET(MAIKO_DISPLAY_X11_DEFINITIONS
-    "-DXWINDOW"
+    "-DXWINDOW -DLOCK_X_UPDATES"
   )
   SET(MAIKO_DISPLAY_X11_LIBRARIES X11::X11)
   SET(MAIKO_DISPLAY_X11_SRCS
diff --git a/bin/makefile-cygwin.x86_64-x b/bin/makefile-cygwin.x86_64-x
index f280cba..8129feb 100644
--- a/bin/makefile-cygwin.x86_64-x
+++ b/bin/makefile-cygwin.x86_64-x
@@ -14,7 +14,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-darwin.386-x b/bin/makefile-darwin.386-x
index 7cb52d3..5125737 100644
--- a/bin/makefile-darwin.386-x
+++ b/bin/makefile-darwin.386-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g
diff --git a/bin/makefile-darwin.aarch64-x b/bin/makefile-darwin.aarch64-x
index a92219f..f8f59e7 100644
--- a/bin/makefile-darwin.aarch64-x
+++ b/bin/makefile-darwin.aarch64-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2
diff --git a/bin/makefile-darwin.ppc-x b/bin/makefile-darwin.ppc-x
index 50db58f..8d35749 100644
--- a/bin/makefile-darwin.ppc-x
+++ b/bin/makefile-darwin.ppc-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/usr/X11/include -DXWINDOW
+XFLAGS = -I/usr/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g
diff --git a/bin/makefile-darwin.x86_64-x b/bin/makefile-darwin.x86_64-x
index e17f10b..0ac392b 100644
--- a/bin/makefile-darwin.x86_64-x
+++ b/bin/makefile-darwin.x86_64-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O1 -g
diff --git a/bin/makefile-init-darwin.386 b/bin/makefile-init-darwin.386
index c7aaa62..fbd168d 100644
--- a/bin/makefile-init-darwin.386
+++ b/bin/makefile-init-darwin.386
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2, for INIT we want unoptimized in case we need to debug it
 OPTFLAGS =  -O0 -g
diff --git a/bin/makefile-init-darwin.aarch64 b/bin/makefile-init-darwin.aarch64
index 1314d4f..c81744d 100644
--- a/bin/makefile-init-darwin.aarch64
+++ b/bin/makefile-init-darwin.aarch64
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
         $(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O0 -g3
diff --git a/bin/makefile-init-darwin.x86_64 b/bin/makefile-init-darwin.x86_64
index 322b4a8..943e903 100644
--- a/bin/makefile-init-darwin.x86_64
+++ b/bin/makefile-init-darwin.x86_64
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/opt/X11/include -DXWINDOW
+XFLAGS = -I/opt/X11/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O0 -g
diff --git a/bin/makefile-init-linux.x86_64 b/bin/makefile-init-linux.x86_64
index 8d696dd..3f64a50 100644
--- a/bin/makefile-init-linux.x86_64
+++ b/bin/makefile-init-linux.x86_64
@@ -14,7 +14,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2, for INIT we want unoptimized in case we need to debug it
 OPTFLAGS =  -O0 -g
diff --git a/bin/makefile-init-sunos5.sparc b/bin/makefile-init-sunos5.sparc
index c8ced0b..69f8997 100644
--- a/bin/makefile-init-sunos5.sparc
+++ b/bin/makefile-init-sunos5.sparc
@@ -30,7 +30,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -g for MAKEINIT, as it needs debugging often.
 OPTFLAGS = -g3 -O0
diff --git a/bin/makefile-linux.386-x b/bin/makefile-linux.386-x
index b25198d..37fb185 100644
--- a/bin/makefile-linux.386-x
+++ b/bin/makefile-linux.386-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-linux.aarch64-x b/bin/makefile-linux.aarch64-x
index 1f2f156..c6db5f1 100644
--- a/bin/makefile-linux.aarch64-x
+++ b/bin/makefile-linux.aarch64-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-linux.armv7l-x b/bin/makefile-linux.armv7l-x
index 1f2f156..c6db5f1 100644
--- a/bin/makefile-linux.armv7l-x
+++ b/bin/makefile-linux.armv7l-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-linux.x86_64-x b/bin/makefile-linux.x86_64-x
index f280cba..8129feb 100644
--- a/bin/makefile-linux.x86_64-x
+++ b/bin/makefile-linux.x86_64-x
@@ -14,7 +14,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-openbsd.x86_64-x b/bin/makefile-openbsd.x86_64-x
index b95e5f5..70a1798 100644
--- a/bin/makefile-openbsd.x86_64-x
+++ b/bin/makefile-openbsd.x86_64-x
@@ -13,7 +13,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xwinman.o
 
 
-XFLAGS = -I/usr/X11R6/include -DXWINDOW
+XFLAGS = -I/usr/X11R6/include -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-sunos5.386-x b/bin/makefile-sunos5.386-x
index b22e33b..f1c7b78 100644
--- a/bin/makefile-sunos5.386-x
+++ b/bin/makefile-sunos5.386-x
@@ -22,7 +22,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g
diff --git a/bin/makefile-sunos5.i386-x b/bin/makefile-sunos5.i386-x
index 74a8bb6..8831073 100644
--- a/bin/makefile-sunos5.i386-x
+++ b/bin/makefile-sunos5.i386-x
@@ -22,7 +22,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-sunos5.sparc-x b/bin/makefile-sunos5.sparc-x
index 931d228..a9304cc 100644
--- a/bin/makefile-sunos5.sparc-x
+++ b/bin/makefile-sunos5.sparc-x
@@ -29,7 +29,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g3
diff --git a/bin/makefile-sunos5.x86_64-x b/bin/makefile-sunos5.x86_64-x
index 923544d..3f8ab9f 100644
--- a/bin/makefile-sunos5.x86_64-x
+++ b/bin/makefile-sunos5.x86_64-x
@@ -22,7 +22,7 @@ XFILES = $(OBJECTDIR)xmkicon.o \
 	$(OBJECTDIR)xrdopt.o \
 	$(OBJECTDIR)xwinman.o
 
-XFLAGS = -DXWINDOW
+XFLAGS = -DXWINDOW -DLOCK_X_UPDATES
 
 # OPTFLAGS is normally -O2.
 OPTFLAGS =  -O2 -g
diff --git a/src/xinit.c b/src/xinit.c
index 938935e..d47c8d9 100644
--- a/src/xinit.c
+++ b/src/xinit.c
@@ -108,13 +108,15 @@ void lisp_Xexit(DspInterface dsp)
 {
   assert(Lisp_Xinitialized);
 
-#if defined(OS5) && defined(I_SETSIG)
+#if defined(I_SETSIG)
   ioctl(ConnectionNumber(dsp->display_id), I_SETSIG, 0); /* so no interrupts happen during */
 #endif
 
+  XLOCK;
   XDestroySubwindows(dsp->display_id, dsp->LispWindow);
   XDestroyWindow(dsp->display_id, dsp->LispWindow);
   XCloseDisplay(dsp->display_id);
+  XUNLOCK(dsp);
 
   Lisp_Xinitialized = false;
 } /* end lisp_Xexit */