diff --git a/ChangeLog b/ChangeLog
index 4100e48c32..2cc9782097 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Wed Aug 24 00:38:22 2011  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* thread.c (update_coverage): skip coverage count up if the current
+	  line is out of the way.  rb_sourceline() is unreliable when source
+	  code is big.  [ruby-dev:44413]
+
+	* test/coverage/test_coverage.rb: add a test for above.
+
 Tue Aug 23 15:23:56 2011  Eric Hodel  <drbrain@segment7.net>
 
 	* load.c (rb_f_require):  Improve documentation of Kernel#require.
diff --git a/test/coverage/test_coverage.rb b/test/coverage/test_coverage.rb
index 56966b1f0e..4d785c3c0e 100644
--- a/test/coverage/test_coverage.rb
+++ b/test/coverage/test_coverage.rb
@@ -31,10 +31,31 @@ class TestCoverage < Test::Unit::TestCase
 
         Coverage.start
         require tmp + '/test.rb'
-        Coverage.result
+        assert_equal 3, Coverage.result[tmp + '/test.rb'].size
         Coverage.start
         coverage_test_method
-        assert_equal 1, Coverage.result.size
+        assert_equal 0, Coverage.result[tmp + '/test.rb'].size
+      }
+    }
+  ensure
+    $".replace loaded_features
+  end
+
+  def test_big_code
+    loaded_features = $".dup
+
+    Dir.mktmpdir {|tmp|
+      Dir.chdir(tmp) {
+        File.open("test.rb", "w") do |f|
+          f.puts "p\n" * 10000
+          f.puts "def ignore(x); end"
+          f.puts "ignore([1"
+          f.puts "])"
+        end
+
+        Coverage.start
+        require tmp + '/test.rb'
+        assert_equal 10003, Coverage.result[tmp + '/test.rb'].size
       }
     }
   ensure
diff --git a/thread.c b/thread.c
index 6970d8f62b..57a69629a6 100644
--- a/thread.c
+++ b/thread.c
@@ -4764,7 +4764,7 @@ update_coverage(rb_event_flag_t event, VALUE proc, VALUE self, ID id, VALUE klas
 	long line = rb_sourceline() - 1;
 	long count;
 	if (RARRAY_PTR(coverage)[line] == Qnil) {
-	    rb_bug("bug");
+	    return;
 	}
 	count = FIX2LONG(RARRAY_PTR(coverage)[line]) + 1;
 	if (POSFIXABLE(count)) {