diff --git a/ChangeLog b/ChangeLog
index 01b455429f..1a50c3da41 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jul 26 15:30:37 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
+
+	* enc/windows_1251.c, test/ruby/enc/test_case_comprehensive.rb:
+	  Implement non-ASCII case conversion for Windows-1251, by Shunsuke Sato.
+
 Tue Jul 26 13:04:59 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* test/ruby/enc/test_case_comprehensive.rb: Add explicit skip test for
diff --git a/enc/windows_1251.c b/enc/windows_1251.c
index b9675cfd8e..0f9b7fa69a 100644
--- a/enc/windows_1251.c
+++ b/enc/windows_1251.c
@@ -180,6 +180,47 @@ cp1251_get_case_fold_codes_by_str(OnigCaseFoldType flag,
 	     flag, p, end, items);
 }
 
+static int
+case_map (OnigCaseFoldType* flagP, const OnigUChar** pp,
+		const OnigUChar* end, OnigUChar* to, OnigUChar* to_end,
+		const struct OnigEncodingTypeST* enc)
+{
+  OnigCodePoint code;
+  OnigUChar *to_start = to;
+  OnigCaseFoldType flags = *flagP;
+
+  while (*pp<end && to<to_end) {
+    code = *(*pp)++;
+    if ((EncCP1251_CtypeTable[code] & BIT_CTYPE_UPPER)
+	     && (flags & (ONIGENC_CASE_DOWNCASE|ONIGENC_CASE_FOLD))) {
+      flags |= ONIGENC_CASE_MODIFIED;
+      code = ENC_CP1251_TO_LOWER_CASE(code);
+    }
+    else if (code==0xB5)  ;
+    else if ((EncCP1251_CtypeTable[code]&BIT_CTYPE_LOWER)
+	     && (flags&ONIGENC_CASE_UPCASE)) {
+      flags |= ONIGENC_CASE_MODIFIED;
+      if ((0x61<=code && code<=0x7A) || (0xE0<=code && code<=0xFF))
+	code -= 0x20;
+      else if (code==0xA2 || code==0xB3 || code==0xBE)
+	code -= 0x01;
+      else if (code==0x83)
+	code = 0x81;
+      else if (code==0xBC)
+	code = 0xA3;
+      else if (code==0xB4)
+	code = 0xA5;
+      else
+	code -= 0x10;
+    }
+    *to++ = code;
+    if (flags&ONIGENC_CASE_TITLECASE)  /* switch from titlecase to lowercase for capitalize */
+      flags ^= (ONIGENC_CASE_UPCASE|ONIGENC_CASE_DOWNCASE|ONIGENC_CASE_TITLECASE);
+  }
+  *flagP = flags;
+  return (int)(to-to_start);
+}
+
 OnigEncodingDefine(windows_1251, Windows_1251) = {
   onigenc_single_byte_mbc_enc_len,
   "Windows-1251",      /* name */
@@ -199,7 +240,7 @@ OnigEncodingDefine(windows_1251, Windows_1251) = {
   onigenc_always_true_is_allowed_reverse_match,
   0,
   ONIGENC_FLAG_NONE,
-  onigenc_single_byte_ascii_only_case_map,
+  case_map,
 };
 /*
  * Name: windows-1251
diff --git a/test/ruby/enc/test_case_comprehensive.rb b/test/ruby/enc/test_case_comprehensive.rb
index 13c61ba7d5..dabe727423 100644
--- a/test/ruby/enc/test_case_comprehensive.rb
+++ b/test/ruby/enc/test_case_comprehensive.rb
@@ -287,7 +287,7 @@ TestComprehensiveCaseFold.data_files_available? and  class TestComprehensiveCase
   generate_ascii_only_case_mapping_tests 'Shift_JIS'
   generate_ascii_only_case_mapping_tests 'Windows-31J'
   generate_ascii_only_case_mapping_tests 'Windows-1250'
-  generate_ascii_only_case_mapping_tests 'Windows-1251'
+  generate_case_mapping_tests 'Windows-1251'
   generate_case_mapping_tests 'Windows-1252'
   generate_ascii_only_case_mapping_tests 'Windows-1253'
   generate_ascii_only_case_mapping_tests 'Windows-1254'