diff --git a/ChangeLog b/ChangeLog
index fce7f4f9a3..0bd05ff231 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Nov 18 18:27:47 2007  Tanaka Akira  <akr@fsij.org>
+
+	* time.c (time_minus): fix Time.at(2**60+1) - Time.at(2**60).
+
 Sun Nov 18 17:28:49 2007  Tanaka Akira  <akr@fsij.org>
 
 	* time.c (time_arg): show actual year in 2-3 digits year warning.
diff --git a/test/ruby/test_time.rb b/test/ruby/test_time.rb
index 6177e198d9..db922e1177 100644
--- a/test/ruby/test_time.rb
+++ b/test/ruby/test_time.rb
@@ -71,4 +71,14 @@ class TestTime < Test::Unit::TestCase
       assert_equal(Time.at(0x7fffffff), Time.at(-0x80000000) - (-0xffffffff))
     end
   end
+
+  def test_big_minus
+    begin
+      bigtime0 = Time.at(2**60)
+      bigtime1 = Time.at(2**60+1)
+    rescue RangeError
+      return
+    end
+    assert_equal(1.0, bigtime1 - bigtime0)
+  end
 end
diff --git a/time.c b/time.c
index 7d09c289e7..dc71a93c07 100644
--- a/time.c
+++ b/time.c
@@ -1320,9 +1320,11 @@ time_minus(VALUE time1, VALUE time2)
 	double f;
 
 	GetTimeval(time2, tobj2);
-	f = (double)tobj->tv.tv_sec - (double)tobj2->tv.tv_sec;
+        if (tobj->tv.tv_sec < tobj2->tv.tv_sec)
+            f = -(double)(unsigned_time_t)(tobj2->tv.tv_sec - tobj->tv.tv_sec);
+        else
+            f = (double)(unsigned_time_t)(tobj->tv.tv_sec - tobj2->tv.tv_sec);
 	f += ((double)tobj->tv.tv_usec - (double)tobj2->tv.tv_usec)*1e-6;
-	/* XXX: should check float overflow on 64bit time_t platforms */
 
 	return DOUBLE2NUM(f);
     }