diff --git a/Source/CFRunLoop.c b/Source/CFRunLoop.c
index 88a4ad2..392b2e6 100644
--- a/Source/CFRunLoop.c
+++ b/Source/CFRunLoop.c
@@ -1587,6 +1587,7 @@ CFRunLoopObserverCreate (CFAllocatorRef  alloc, CFOptionFlags activities,
   if (new)
     {
       GSMutexInitialize (&(new->_lock));
+      new->_isValid = true;
       new->_activities = activities;
       new->_repeats = repeats;
       new->_order = order;
diff --git a/Tests/CFRunLoop/observer_valid.m b/Tests/CFRunLoop/observer_valid.m
new file mode 100644
index 0000000..e545995
--- /dev/null
+++ b/Tests/CFRunLoop/observer_valid.m
@@ -0,0 +1,22 @@
+#include "CoreFoundation/CFRunLoop.h"
+#include "../CFTesting.h"
+
+static void
+observe (CFRunLoopObserverRef o, CFRunLoopActivity a, void *info)
+{
+}
+
+int main (void)
+{
+  CFRunLoopObserverRef obs = CFRunLoopObserverCreate (NULL,
+    kCFRunLoopBeforeWaiting, false, 0, observe, NULL);
+
+  PASS_CF (CFRunLoopObserverIsValid (obs) == true, "A new observer is valid.");
+
+  CFRunLoopObserverInvalidate (obs);
+  PASS_CF (CFRunLoopObserverIsValid (obs) == false,
+    "An invalidated observer is no longer valid.");
+
+  CFRelease (obs);
+  return 0;
+}