diff --git a/basis/core-foundation/run-loop/run-loop.factor b/basis/core-foundation/run-loop/run-loop.factor
index 2370dd4562..e2ba06d61f 100644
--- a/basis/core-foundation/run-loop/run-loop.factor
+++ b/basis/core-foundation/run-loop/run-loop.factor
@@ -91,6 +91,9 @@ TUPLE: run-loop fds sources timers ;
         CFRunLoopAddTimer
     ] bi ;
 
+: invalidate-run-loop-timers ( -- )
+    run-loop [ [ [ CFRunLoopTimerInvalidate ] [ CFRelease ] bi ] each V{ } ] change-timers drop ;
+
 <PRIVATE
 
 : ((reset-timer)) ( timer counter timestamp -- )
diff --git a/basis/ui/backend/cocoa/cocoa.factor b/basis/ui/backend/cocoa/cocoa.factor
index 6e64c35e49..d4f9b82cff 100644
--- a/basis/ui/backend/cocoa/cocoa.factor
+++ b/basis/ui/backend/cocoa/cocoa.factor
@@ -214,6 +214,7 @@ M: cocoa-ui-backend beep ( -- )
     NSBeep ;
 
 M: cocoa-ui-backend system-alert
+    invalidate-run-loop-timers
     NSAlert -> alloc -> init -> autorelease [
         {
             [ swap <NSString> -> setInformativeText: ]
@@ -221,7 +222,8 @@ M: cocoa-ui-backend system-alert
             [ "OK" <NSString> -> addButtonWithTitle: drop ]
             [ -> runModal drop ]
         } cleave
-    ] [ 2drop ] if* ;
+    ] [ 2drop ] if*
+    init-thread-timer ;
 
 CLASS: {
     { +superclass+ "NSObject" }