diff --git a/Source/CFRunLoop.c b/Source/CFRunLoop.c
index 88a4ad2..f148b0e 100644
--- a/Source/CFRunLoop.c
+++ b/Source/CFRunLoop.c
@@ -1845,8 +1845,8 @@ CFRunLoopTimerSetNextFireDate (CFRunLoopTimerRef timer,
     }
   
   timer->_nextFireDate = fireDate;
-  // Wake up the runloop so that it can recalculate the next timer date
-  // but since timers should be planned on current runloop only (NSTimer
-  // says so), this may not be necessary.
-  CFRunLoopWakeUp(timer->_runloop);
+  // Wake up the runloop so that it can recalculate the next timer date,
+  // but only if the timer has been added to one.
+  if (timer->_runloop != NULL)
+    CFRunLoopWakeUp(timer->_runloop);
 }
diff --git a/Tests/CFRunLoop/timer_setfiredate.m b/Tests/CFRunLoop/timer_setfiredate.m
new file mode 100644
index 0000000..32d869d
--- /dev/null
+++ b/Tests/CFRunLoop/timer_setfiredate.m
@@ -0,0 +1,20 @@
+#include "CoreFoundation/CFRunLoop.h"
+#include "../CFTesting.h"
+
+static void
+fire (CFRunLoopTimerRef t, void *info)
+{
+}
+
+int main (void)
+{
+  CFRunLoopTimerRef t = CFRunLoopTimerCreate (NULL, 100.0, 5.0, 0, 0,
+    fire, NULL);
+
+  CFRunLoopTimerSetNextFireDate (t, 250.0);
+  PASS_CF (CFRunLoopTimerGetNextFireDate (t) == 250.0,
+    "Setting the fire date of a timer not in a run loop updates it.");
+
+  CFRelease (t);
+  return 0;
+}