diff --git a/dix/dispatch.c b/dix/dispatch.c
index 0fed6a0e7..99103ae65 100644
--- a/dix/dispatch.c
+++ b/dix/dispatch.c
@@ -157,8 +157,14 @@ static int nextFreeClientID; /* always MIN free client ID */
 static int	nClients;	/* number of authorized clients */
 
 CallbackListPtr ClientStateCallback;
-char dispatchException = 0;
-char isItTimeToYield;
+
+/* dispatchException & isItTimeToYield must be declared volatile since they
+ * are modified by signal handlers - otherwise optimizer may assume it doesn't
+ * need to actually check value in memory when used and may miss changes from
+ * signal handlers.
+ */
+volatile char dispatchException = 0;
+volatile char isItTimeToYield;
 
 /* Various of the DIX function interfaces were not designed to allow
  * the client->errorValue to be set on BadValue and other errors.
diff --git a/include/opaque.h b/include/opaque.h
index 8d7408f8a..277ca61ac 100644
--- a/include/opaque.h
+++ b/include/opaque.h
@@ -42,8 +42,8 @@ from The Open Group.
 extern char *defaultTextFont;
 extern char *defaultCursorFont;
 extern int MaxClients;
-extern char isItTimeToYield;
-extern char dispatchException;
+extern volatile char isItTimeToYield;
+extern volatile char dispatchException;
 
 /* bit values for dispatchException */
 #define DE_RESET     1