diff --git a/ChangeLog b/ChangeLog
index 301661399..5c9fda290 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2008-07-02  Richard Frith-Macdonald <rfm@gnu.org>
+
+	* Source/NSIndexSet.m: Implement ([-countOfIndexesInRange:])
+
 2008-06-30  Richard Frith-Macdonald <rfm@gnu.org>
 
         * Source/GSFFIInvocation.m:
diff --git a/Source/NSIndexSet.m b/Source/NSIndexSet.m
index 277cc5b74..8794adbdc 100644
--- a/Source/NSIndexSet.m
+++ b/Source/NSIndexSet.m
@@ -234,7 +234,26 @@ static unsigned posForIndex(GSIArray array, unsigned index)
 
 - (NSUInteger) countOfIndexesInRange: (NSRange)range
 {
-  return 0;
+  if (_array == 0 || GSIArrayCount(_array) == 0)
+    {
+      return 0;
+    }
+  else
+    {
+      unsigned	count = GSIArrayCount(_array);
+      unsigned	total = 0;
+      unsigned	i = 0;
+
+      while (i < count)
+	{
+	  NSRange	r = GSIArrayItemAtIndex(_array, i).ext;
+          
+          r = NSIntersectionRange(r, range);
+	  total += r.length;
+	  i++;
+	}
+      return total;
+    }
 }
 
 - (void) dealloc