diff --git a/hash.c b/hash.c
index af094cca90..3a84a94714 100644
--- a/hash.c
+++ b/hash.c
@@ -2143,15 +2143,26 @@ keys_i(VALUE key, VALUE value, VALUE ary)
     return ST_CONTINUE;
 }
 
+static int
+keys_block_i(VALUE key, VALUE value, VALUE ary)
+{
+    if (RTEST(rb_yield(key))) {
+        rb_ary_push(ary, key);
+    }
+    return ST_CONTINUE;
+}
+
 /*
  *  call-seq:
  *     hsh.keys    -> array
  *
  *  Returns a new array populated with the keys from this hash. See also
- *  <code>Hash#values</code>.
+ *  <code>Hash#values</code>. If a block is given, it returns the keys for
+ *  which the block evaluates to +true+.
  *
  *     h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
- *     h.keys   #=> ["a", "b", "c", "d"]
+ *     h.keys                                 #=> ["a", "b", "c", "d"]
+ #     h.keys { |key| %w[a c].include?(key) } #=> ["a", "c"]
  *
  */
 
@@ -2162,19 +2173,27 @@ rb_hash_keys(VALUE hash)
     st_index_t size = RHASH_SIZE(hash);
 
     keys = rb_ary_new_capa(size);
-    if (size == 0) return keys;
 
-    if (ST_DATA_COMPATIBLE_P(VALUE)) {
-	st_table *table = RHASH(hash)->ntbl;
+    if (size == 0) return keys;
 
-	rb_gc_writebarrier_remember(keys);
-	RARRAY_PTR_USE(keys, ptr, {
-	    size = st_keys(table, ptr, size);
-	});
-	rb_ary_set_len(keys, size);
+    if (rb_block_given_p()) {
+        rb_hash_foreach(hash, keys_block_i, keys);
     }
     else {
-	rb_hash_foreach(hash, keys_i, keys);
+        if (ST_DATA_COMPATIBLE_P(VALUE)) {
+            st_table *table = RHASH(hash)->ntbl;
+
+            rb_gc_writebarrier_remember(keys);
+
+            RARRAY_PTR_USE(keys, ptr, {
+                size = st_keys(table, ptr, size);
+            });
+
+            rb_ary_set_len(keys, size);
+        }
+        else {
+            rb_hash_foreach(hash, keys_i, keys);
+        }
     }
 
     return keys;
diff --git a/spec/ruby/core/hash/keys_spec.rb b/spec/ruby/core/hash/keys_spec.rb
index 9a067085e5..9c046bd544 100644
--- a/spec/ruby/core/hash/keys_spec.rb
+++ b/spec/ruby/core/hash/keys_spec.rb
@@ -20,4 +20,11 @@
       h[h.keys[i]].should == h.values[i]
     end
   end
+
+  it "accepts a block" do
+    h = { 1 => "1", 2 => "2", 3 => "3", 4 => "4" }
+
+    h.keys { |key| key.odd?  }.should == [1, 3]
+    h.keys { |key| key.even? }.should == [2, 4]
+  end
 end