diff --git a/dlls/kernel32/locale.c b/dlls/kernel32/locale.c
index 0f370273a98..4d1eac6ebee 100644
--- a/dlls/kernel32/locale.c
+++ b/dlls/kernel32/locale.c
@@ -3557,8 +3557,16 @@ INT WINAPI LCMapStringEx(LPCWSTR name, DWORD flags, LPCWSTR src, INT srclen, LPW
         else if (flags & LCMAP_HALFWIDTH)
         {
             for (len = 0; srclen; src++, srclen--, len++)
-                if (decompose_katakana(*src, NULL, 0) == 2)
+            {
+                WCHAR wch = *src;
+                /* map Hiragana to Katakana before decomposition if needed */
+                if ((flags & LCMAP_KATAKANA) &&
+                    ((wch >= 0x3041 && wch <= 0x3096) || wch == 0x309D || wch == 0x309E))
+                    wch += 0x60;
+
+                if (decompose_katakana(wch, NULL, 0) == 2)
                     len++;
+            }
         }
         else
             len = srclen;
diff --git a/dlls/kernel32/tests/locale.c b/dlls/kernel32/tests/locale.c
index b8ced500f6d..d3eb2ecf15e 100644
--- a/dlls/kernel32/tests/locale.c
+++ b/dlls/kernel32/tests/locale.c
@@ -2537,7 +2537,6 @@ static void test_lcmapstring_unicode(lcmapstring_wrapper func_ptr, const char *f
     ok(!lstrcmpW(buf, halfwidth_text2), "%s string compare mismatch\n", func_name);
 
     ret2 = func_ptr(LCMAP_HALFWIDTH | LCMAP_KATAKANA, japanese_text, -1, NULL, 0);
-    todo_wine
     ok(ret == ret2, "%s ret %d, expected value %d\n", func_name, ret, ret2);
 
     /* test buffer overflow */