diff --git a/string.c b/string.c
index 6988e08..8b508bf 100644
--- a/string.c
+++ b/string.c
@@ -3192,6 +3192,24 @@ rb_str_casecmp(VALUE str1, VALUE str2)
     return INT2FIX(-1);
 }
 
+/*
+ *  call-seq:
+ *     str.casecmp?(other_str)   -> true or false
+ *
+ *  Case-insensitive string comparison.
+ *
+ *     "abcdef".casecmp?("abcde")     #=> false
+ *     "aBcDeF".casecmp?("abcdef")    #=> true
+ *     "abcdef".casecmp?("abcdefg")   #=> false
+ *     "abcdef".casecmp?("ABCDEF")    #=> true
+ */
+
+static VALUE
+rb_str_casecmp_p(VALUE str1, VALUE str2)
+{
+    return rb_str_casecmp(str1, str2) == INT2FIX(0) ? Qtrue : Qfalse;
+}
+
 #define rb_str_index(str, sub, offset) rb_strseq_index(str, sub, offset, 0)
 
 static long
@@ -9604,6 +9622,22 @@ sym_casecmp(VALUE sym, VALUE other)
 }
 
 /*
+ *  call-seq:
+ *     sym.casecmp?(other)  -> true, false, or nil
+ *
+ *  Case-insensitive symbol comparison.
+ */
+
+static VALUE
+sym_casecmp_p(VALUE sym, VALUE other)
+{
+    if (!SYMBOL_P(other)) {
+        return Qnil;
+    }
+    return sym_casecmp(sym, other) == INT2FIX(0) ? Qtrue : Qfalse;
+}
+
+/*
  * call-seq:
  *   sym =~ obj   -> integer or nil
  *
@@ -9802,6 +9836,7 @@ Init_String(void)
     rb_define_method(rb_cString, "eql?", rb_str_eql, 1);
     rb_define_method(rb_cString, "hash", rb_str_hash_m, 0);
     rb_define_method(rb_cString, "casecmp", rb_str_casecmp, 1);
+    rb_define_method(rb_cString, "casecmp?", rb_str_casecmp_p, 1);
     rb_define_method(rb_cString, "+", rb_str_plus, 1);
     rb_define_method(rb_cString, "*", rb_str_times, 1);
     rb_define_method(rb_cString, "%", rb_str_format_m, 1);
@@ -9951,6 +9986,7 @@ Init_String(void)
 
     rb_define_method(rb_cSymbol, "<=>", sym_cmp, 1);
     rb_define_method(rb_cSymbol, "casecmp", sym_casecmp, 1);
+    rb_define_method(rb_cSymbol, "casecmp?", sym_casecmp_p, 1);
     rb_define_method(rb_cSymbol, "=~", sym_match, 1);
 
     rb_define_method(rb_cSymbol, "[]", sym_aref, -1);
diff --git a/test/ruby/enc/test_utf16.rb b/test/ruby/enc/test_utf16.rb
index 99b48c2..865c465 100644
--- a/test/ruby/enc/test_utf16.rb
+++ b/test/ruby/enc/test_utf16.rb
@@ -138,6 +138,12 @@ def test_casecmp
     assert_not_equal(0, s1.casecmp(s2), "#{encdump s1}.casecmp(#{encdump s2})")
   end
 
+  def test_casecmp?
+    s1 = "aa".force_encoding("utf-16be")
+    s2 = "AA"
+    assert_not_equal(true, s1.casecmp?(s2), "#{encdump s1}.casecmp?(#{encdump s2})")
+  end
+
   def test_end_with
     s1 = "ab".force_encoding("utf-16be")
     s2 = "b".force_encoding("utf-16be")
@@ -382,4 +388,11 @@ def test_casecmp2
     a = ary.sort {|x,y| x.casecmp(y) }
     assert_equal(e, a)
   end
+
+  def test_casecmp2?
+    assert_equal(true, "\0A".force_encoding("UTF-16BE").casecmp?("\0a".force_encoding("UTF-16BE")))
+    assert_not_equal(true, "\0A".force_encoding("UTF-16LE").casecmp?("\0a".force_encoding("UTF-16LE")))
+    assert_not_equal(true, "A\0".force_encoding("UTF-16BE").casecmp?("a\0".force_encoding("UTF-16BE")))
+    assert_equal(true, "A\0".force_encoding("UTF-16LE").casecmp?("a\0".force_encoding("UTF-16LE")))
+  end
 end
diff --git a/test/ruby/test_m17n.rb b/test/ruby/test_m17n.rb
index 950d205..033fdb0 100644
--- a/test/ruby/test_m17n.rb
+++ b/test/ruby/test_m17n.rb
@@ -1155,6 +1155,12 @@ def test_casecmp
     assert_not_equal(0, s1.casecmp(s2))
   end
 
+  def test_casecmp?
+    s1 = s("\x81\x41")
+    s2 = s("\x81\x61")
+    assert_not_equal(true, s1.casecmp?(s2))
+  end
+
   def test_reverse
     bug11387 = '[ruby-dev:49189] [Bug #11387]'
     s1 = u("abcdefghij\xf0")
diff --git a/test/ruby/test_m17n_comb.rb b/test/ruby/test_m17n_comb.rb
index 99c162a..1f2f8b1 100644
--- a/test/ruby/test_m17n_comb.rb
+++ b/test/ruby/test_m17n_comb.rb
@@ -593,6 +593,14 @@ def test_str_casecmp
     }
   end
 
+  def test_str_casecmp?
+    combination(STRINGS, STRINGS) {|s1, s2|
+      next unless s1.valid_encoding? && s2.valid_encoding? && Encoding.compatible?(s1, s2)
+      r = s1.casecmp?(s2)
+      assert_equal(s1.casecmp(s2) == 0, r)
+    }
+  end
+
   def test_str_center
     combination(STRINGS, [0,1,2,3,10]) {|s1, width|
       t = s1.center(width)
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index b1d795e..bde5c21 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -2210,6 +2210,10 @@ def test_casecmp
     assert_equal(1, "\u3042B".casecmp("\u3042a"))
   end
 
+  def test_casecmp?
+    assert_equal(false, "\u3042B".casecmp?("\u3042a"))
+  end
+
   def test_upcase2
     assert_equal("\u3042AB", "\u3042aB".upcase)
   end
diff --git a/test/ruby/test_symbol.rb b/test/ruby/test_symbol.rb
index d8c91c1..999d240 100644
--- a/test/ruby/test_symbol.rb
+++ b/test/ruby/test_symbol.rb
@@ -276,6 +276,13 @@ def test_casecmp
     assert_nil(:foo.casecmp("foo"))
   end
 
+  def test_casecmp?
+    assert_equal(true, :FoO.casecmp?(:fOO))
+    assert_equal(false, :FoO.casecmp?(:BaR))
+    assert_equal(false, :baR.casecmp?(:FoO))
+    assert_nil(:foo.casecmp?("foo"))
+  end
+
   def test_length
     assert_equal(3, :FoO.length)
     assert_equal(3, :FoO.size)