diff --git a/dlls/kernel32/tests/codepage.c b/dlls/kernel32/tests/codepage.c
index 96dd45dc53b..13f9b75291e 100644
--- a/dlls/kernel32/tests/codepage.c
+++ b/dlls/kernel32/tests/codepage.c
@@ -385,7 +385,6 @@ static void test_undefined_byte_char(void)
         ret = MultiByteToWideChar(testset[i].codepage, MB_ERR_INVALID_CHARS,
                                   testset[i].str, -1, NULL, 0);
         if (testset[i].is_error) {
-            todo_wine
             ok(ret == 0 && GetLastError() == ERROR_NO_UNICODE_TRANSLATION,
                "ret is %d, GetLastError is %u (cp %d)\n",
                ret, GetLastError(), testset[i].codepage);
diff --git a/libs/wine/mbtowc.c b/libs/wine/mbtowc.c
index 8b06a89d8ec..1995b31a227 100644
--- a/libs/wine/mbtowc.c
+++ b/libs/wine/mbtowc.c
@@ -39,6 +39,13 @@ static int get_decomposition( WCHAR src, WCHAR *dst, unsigned int dstlen )
     return res;
 }
 
+/* check the code whether it is in Unicode Private Use Area (PUA). */
+/* MB_ERR_INVALID_CHARS raises an error converting from 1-byte character to PUA. */
+static inline int is_private_use_area_char(WCHAR code)
+{
+    return (code >= 0xe000 && code <= 0xf8ff);
+}
+
 /* check src string for invalid chars; return non-zero if invalid char found */
 static inline int check_invalid_chars_sbcs( const struct sbcs_table *table, int flags,
                                             const unsigned char *src, unsigned int srclen )
@@ -49,7 +56,8 @@ static inline int check_invalid_chars_sbcs( const struct sbcs_table *table, int
                                                      + (def_unicode_char & 0xff)];
     while (srclen)
     {
-        if (cp2uni[*src] == def_unicode_char && *src != def_char) break;
+        if ((cp2uni[*src] == def_unicode_char && *src != def_char) ||
+            is_private_use_area_char(cp2uni[*src])) break;
         src++;
         srclen--;
     }
@@ -167,7 +175,8 @@ static inline int check_invalid_chars_dbcs( const struct dbcs_table *table,
             src++;
             srclen--;
         }
-        else if (cp2uni[*src] == def_unicode_char && *src != def_char) break;
+        else if ((cp2uni[*src] == def_unicode_char && *src != def_char) ||
+                 is_private_use_area_char(cp2uni[*src])) break;
         src++;
         srclen--;
     }