diff --git a/ChangeLog b/ChangeLog
index 117bd074a8..c5ac925b61 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Oct 24 08:18:14 2011  Tanaka Akira  <akr@fsij.org>
+
+	* io.c (copy_stream_fallback_body): check nil for EOF of read method.
+	  patch by Eric Wong.  [ruby-core:39134] [Bug #5237]
+
 Sun Oct 23 18:21:23 2011  Kazuki Tsujimoto  <kazuki@callcc.net>
 
 	* ext/tk/MANUAL_tcltklib.eng: fix typo.
diff --git a/io.c b/io.c
index c9a33f3aad..15e2ec982b 100644
--- a/io.c
+++ b/io.c
@@ -8998,7 +8998,10 @@ copy_stream_fallback_body(VALUE arg)
             l = buflen < rest ? buflen : (long)rest;
         }
         if (stp->src_fd == -1) {
-            rb_funcall(stp->src, read_method, 2, INT2FIX(l), buf);
+            VALUE rc = rb_funcall(stp->src, read_method, 2, INT2FIX(l), buf);
+
+            if (read_method == id_read && NIL_P(rc))
+                break;
         }
         else {
             ssize_t ss;
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index e3bbd245ed..c2eecb7397 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -826,6 +826,28 @@ class TestIO < Test::Unit::TestCase
     }
   end
 
+  class Bug5237
+    attr_reader :count
+    def initialize
+      @count = 0
+    end
+
+    def read(bytes, buffer)
+      @count += 1
+      buffer.replace "this is a test"
+      nil
+    end
+  end
+
+  def test_copy_stream_broken_src_read_eof
+    src = Bug5237.new
+    dst = StringIO.new
+    assert_equal 0, src.count
+    th = Thread.new { IO.copy_stream(src, dst) }
+    flunk("timeout") unless th.join(10)
+    assert_equal 1, src.count
+  end
+
   def test_copy_stream_dst_rbuf
     mkcdtmpdir {
       pipe(proc do |w|