diff --git a/texk/bibtex-x/ChangeLog b/texk/bibtex-x/ChangeLog
index 83647045d1..f13181f878 100644
--- a/texk/bibtex-x/ChangeLog
+++ b/texk/bibtex-x/ChangeLog
@@ -1,3 +1,12 @@
+2023-07-08  TANAKA Takuji  <ttk@t-lab.opal.ne.jp>
+
+	* utils.c, gblprocs.h:
+	Enable to build with system ICU DLL icu.dll
+	for Windows 10 version 1903 (May 2019 Update) or later.
+	https://learn.microsoft.com/en-us/windows/win32/intl/international-components-for-unicode--icu-
+	* bibtex-{1,4}.c:
+	Enable to build with older ICU.
+
 2023-04-12  Karl Berry  <karl@freefriends.org>
 
 	* tests/bibtex8.test,
diff --git a/texk/bibtex-x/bibtex-1.c b/texk/bibtex-x/bibtex-1.c
index 29ca1c4654..1f3619a8d7 100644
--- a/texk/bibtex-x/bibtex-1.c
+++ b/texk/bibtex-x/bibtex-1.c
@@ -330,8 +330,10 @@ BEGIN
             case UBLOCK_LATIN_EXTENDED_C:
             case UBLOCK_LATIN_EXTENDED_D:
             case UBLOCK_LATIN_EXTENDED_E:
+#if defined(UBLOCK_LATIN_EXTENDED_G)
             case UBLOCK_LATIN_EXTENDED_F:
             case UBLOCK_LATIN_EXTENDED_G:
+#endif
             case UBLOCK_LATIN_EXTENDED_ADDITIONAL:
             case UBLOCK_GREEK:
             case UBLOCK_GREEK_EXTENDED:
diff --git a/texk/bibtex-x/bibtex-4.c b/texk/bibtex-x/bibtex-4.c
index 9663f5a6b8..0c5bca2536 100644
--- a/texk/bibtex-x/bibtex-4.c
+++ b/texk/bibtex-x/bibtex-4.c
@@ -2818,7 +2818,9 @@ BEGIN
           case UBLOCK_CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D:
           case UBLOCK_CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E:
           case UBLOCK_CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F:
+#if defined(UBLOCK_CJK_UNIFIED_IDEOGRAPHS_EXTENSION_G)
           case UBLOCK_CJK_UNIFIED_IDEOGRAPHS_EXTENSION_G:
+#endif
             string_width |= 0x001;
             break;
       /* kana */
@@ -2826,8 +2828,12 @@ BEGIN
           case UBLOCK_KATAKANA:
           case UBLOCK_KATAKANA_PHONETIC_EXTENSIONS:
           case UBLOCK_KANA_EXTENDED_A:
+#if defined(UBLOCK_KANA_EXTENDED_B)
           case UBLOCK_KANA_EXTENDED_B:
+#endif
+#if defined(UBLOCK_SMALL_KANA_EXTENSION)
           case UBLOCK_SMALL_KANA_EXTENSION:
+#endif
             string_width |= 0x002;
             break;
       /* hangul */
diff --git a/texk/bibtex-x/gblprocs.h b/texk/bibtex-x/gblprocs.h
index 723da15b8d..d82cf703fe 100644
--- a/texk/bibtex-x/gblprocs.h
+++ b/texk/bibtex-x/gblprocs.h
@@ -92,10 +92,14 @@
 
 
 #ifdef UTF_8
+#if defined(WIN32) && defined(WITH_SYSTEM_ICU)
+#include "icu.h"
+#else
 #include "unicode/uchar.h"
 #include "unicode/ustdio.h"
 #include "unicode/ustring.h"
 #include "unicode/ucol.h"
+#endif
 int32_t                 icu_toUChars (BufType_T buf,
                                       BufPointer_T bf_ptr,
                                       BufPointer_T len,
diff --git a/texk/bibtex-x/utils.c b/texk/bibtex-x/utils.c
index 0dd077d8b8..fec5faba96 100644
--- a/texk/bibtex-x/utils.c
+++ b/texk/bibtex-x/utils.c
@@ -121,7 +121,9 @@
 
 #include <stdarg.h>
 #ifdef WIN32
+#if !defined(_MSC_VER)
 #include <getopt.h>
+#endif
 #else
 #include <unistd.h>
 #endif
@@ -133,7 +135,7 @@
 #include <kpathsea/paths.h>
 #include <kpathsea/variable.h>
 #include <kpathsea/lib.h>
-#ifndef WIN32
+#if !defined(WIN32) || defined(_MSC_VER)
 #include <kpathsea/getopt.h>
 #endif
 #endif