diff --git a/ChangeLog b/ChangeLog
index 187e10f4f9..d1d199dd59 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Dec 11 17:59:05 2015  Eric Wong  <e@80x24.org>
+
+	* insns.def (opt_case_dispatch): avoid converting Infinity
+	* test/ruby/test_optimization.rb (test_opt_case_dispatch_inf): new
+	  [ruby-dev:49423] [Bug #11804]'
+
 Fri Dec 11 16:48:57 2015  Eric Wong  <e@80x24.org>
 
 	* hash.c (rb_num_hash_start): avoid pathological behavior
diff --git a/insns.def b/insns.def
index 3c185bd084..df65aa8efd 100644
--- a/insns.def
+++ b/insns.def
@@ -1262,7 +1262,7 @@ opt_case_dispatch
     switch(TYPE(key)) {
       case T_FLOAT: {
 	double ival;
-	if (modf(RFLOAT_VALUE(key), &ival) == 0.0) {
+	if (modf(RFLOAT_VALUE(key), &ival) == 0.0 && !isinf(ival)) {
 	    key = FIXABLE(ival) ? LONG2FIX((long)ival) : rb_dbl2big(ival);
 	}
       }
diff --git a/test/ruby/test_optimization.rb b/test/ruby/test_optimization.rb
index 1c50044f7f..3573d1267f 100644
--- a/test/ruby/test_optimization.rb
+++ b/test/ruby/test_optimization.rb
@@ -362,4 +362,15 @@ class TestRubyOptimization < Test::Unit::TestCase
       assert_redefine_method(k, '===', "assert_equal(#{v.inspect} === 0, 0)")
     end
   end
+
+  def test_opt_case_dispatch_inf
+    inf = 1.0/0.0
+    result = case inf
+             when 1 then 1
+             when 0 then 0
+             else
+               inf.to_i rescue nil
+             end
+    assert_nil result, '[ruby-dev:49423] [Bug #11804]'
+  end
 end