diff --git a/ChangeLog b/ChangeLog
index aa1c41a328..fa2db35eee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Apr  7 21:35:08 2008  Akinori MUSHA  <knu@iDaemons.org>
+
+	* array.c (rb_ary_nitems): Backport Array#nitems with a block;
+	  suggested by Bertram Scharpf <lists@bertram-scharpf.de> in
+	  [ruby-talk:134083].
+
 Sun Apr  6 09:45:00 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* dir.c (dir_tell): check if closed.  [ruby-core:16223]
diff --git a/NEWS b/NEWS
index 74b552c6f2..82f327030f 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,10 @@ with all sufficient information, see the ChangeLog file.
 
 * builtin classes
 
+  * Array#nitems now takes a block optionally, which is used to
+    determine if each element should be counted instead of checking if
+    the element is non-nil.
+
   * Integer#ord implemented.
   * Integer#odd? implemented.
   * Integer#even? implemented.
diff --git a/array.c b/array.c
index c3aeefe372..2d345dab5d 100644
--- a/array.c
+++ b/array.c
@@ -2856,11 +2856,16 @@ rb_ary_compact(ary)
 /*
  *  call-seq:
  *     array.nitems -> int
+ *     array.nitems { |item| block }  -> int
  *  
  *  Returns the number of non-<code>nil</code> elements in _self_.
+ *  If a block is given, the elements yielding a true value are
+ *  counted.
+ *
  *  May be zero.
  *     
  *     [ 1, nil, 3, nil, 5 ].nitems   #=> 3
+ *     [5,6,7,8,9].nitems { |x| x % 2 != 0 }  #=> 3
  */
 
 static VALUE
@@ -2868,14 +2873,23 @@ rb_ary_nitems(ary)
     VALUE ary;
 {
     long n = 0;
-    VALUE *p, *pend;
+ 
+    if (rb_block_given_p()) {
+	long i;
 
-    p = RARRAY(ary)->ptr;
-    pend = p + RARRAY(ary)->len;
+	for (i=0; i<RARRAY_LEN(ary); i++) {
+	    VALUE v = RARRAY_PTR(ary)[i];
+ 	    if (RTEST(rb_yield(v))) n++;
+ 	}
+    }
+    else {
+	VALUE *p = RARRAY_PTR(ary);
+	VALUE *pend = p + RARRAY_LEN(ary);
 
-    while (p < pend) {
-	if (!NIL_P(*p)) n++;
-	p++;
+ 	while (p < pend) {
+ 	    if (!NIL_P(*p)) n++;
+ 	    p++;
+ 	}
     }
     return LONG2NUM(n);
 }