diff --git a/.gitignore b/.gitignore
index 33f7bda..844a299 100755
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@
 *.kpf
 *.svg
 *.db
+.idea/*
 barcode/__pycache*
 build/*
 dist/*
diff --git a/barcode/codex.py b/barcode/codex.py
index ef72187..213a9fb 100755
--- a/barcode/codex.py
+++ b/barcode/codex.py
@@ -139,7 +139,7 @@ class Code128(Barcode):
     def __init__(self, code, writer=None) -> None:
         self.code = code
         self.writer = writer or self.default_writer()
-        self._charset = "B"
+        self._charset = "C"
         self._buffer = ""
         check_code(self.code, self.name, code128.ALL)
 
@@ -163,9 +163,15 @@ def _new_charset(self, which):
         self._charset = which
         return [code]
 
+    # to be redefined in subclass if required
+    def _is_char_FNC1_CHAR(self, char):
+        # FNC1 char is defined in GS1-128 specification and it is defined just the same for all encodings
+        # therefore this sing should be treated in a special way.
+        return False
+
     def _maybe_switch_charset(self, pos):
         char = self.code[pos]
-        next_ = self.code[pos : pos + 10]
+        next_ = self.code[pos: pos + 10]
 
         def look_next():
             digits = 0
@@ -178,13 +184,16 @@ def look_next():
 
         codes = []
         if self._charset == "C" and not char.isdigit():
-            if char in code128.B:
-                codes = self._new_charset("B")
-            elif char in code128.A:
-                codes = self._new_charset("A")
-            if len(self._buffer) == 1:
-                codes.append(self._convert(self._buffer[0]))
-                self._buffer = ""
+            if self._is_char_FNC1_CHAR(char) and not self._buffer:
+                return codes
+            else:
+                if char in code128.B:
+                    codes = self._new_charset("B")
+                elif char in code128.A:
+                    codes = self._new_charset("A")
+                if len(self._buffer) == 1:
+                    codes.append(self._convert(self._buffer[0]))
+                    self._buffer = ""
         elif self._charset == "B":
             if look_next():
                 codes = self._new_charset("C")
@@ -275,6 +284,9 @@ def __init__(self, code, writer=None) -> None:
     def get_fullcode(self):
         return super().get_fullcode()[1:]
 
+    def _is_char_FNC1_CHAR(self, char):
+        return char == self.FNC1_CHAR
+
 
 # For pre 0.8 compatibility
 PZN = PZN7
diff --git a/tests/test_Gs1_128.py b/tests/test_Gs1_128.py
new file mode 100644
index 0000000..25e0ac8
--- /dev/null
+++ b/tests/test_Gs1_128.py
@@ -0,0 +1,50 @@
+import pytest
+import sys
+import os.path
+sys.path.append(os.path.join(os.path.dirname(__file__), '..'))
+from barcode.codex import Gs1_128
+
+FNC1_CHAR = "\xf1"
+FNC1 = 102
+START_B = 104
+START_C = 105
+FROM_AC_TO_B = 100
+FROM_AB_TO_C = 99
+FROM_BC_TO_A = 101
+CODE_BUILD_TEST = (
+    # '(01)01234567891011(11)200622(17)240622(21)88888888'
+    ('010123456789101111200622172406222188888888', [START_C, FNC1, 1, 1, 23, 45, 67, 89, 10, 11,
+                                                    11, 20, 6, 22,
+                                                    17, 24, 6, 22,
+                                                    21, 88, 88, 88, 88],),
+    # '(01)01234567891011(11)200622(17)240622(21)888888888'
+    ('0101234567891011112006221724062221888888888', [START_C, FNC1, 1, 1, 23, 45, 67, 89, 10, 11,
+                                                     11, 20, 6, 22,
+                                                     17, 24, 6, 22,
+                                                     21, 88, 88, 88, 88, 100, 24],),
+    # '(01)01234567891011(11)200622(10)12345(21)1234'
+    ('0101234567891011112006221012345' + FNC1_CHAR + '211234', [START_C, FNC1, 1, 1, 23, 45, 67, 89, 10, 11,
+                                                                11, 20, 6, 22,
+                                                                10, 12, 34, FROM_AC_TO_B, 21, FNC1,
+                                                                FROM_AB_TO_C, 21, 12, 34],),
+    # '(01)01234567891011(11)200622(10)1234(21)1234'
+    ('010123456789101111200622101234' + FNC1_CHAR + '211234', [START_C, FNC1, 1, 1, 23, 45, 67, 89, 10, 11,
+                                                               11, 20, 6, 22,
+                                                               10, 12, 34, FNC1,
+                                                               21, 12, 34],),
+    # '(01)01234567891011(11)200622(10)240622(21)888888888'
+    ('01012345678910111120062210240622' + FNC1_CHAR + '21888888888', [START_C, FNC1, 1, 1, 23, 45, 67, 89, 10, 11,
+                                                                      11, 20, 6, 22,
+                                                                      10, 24, 6, 22, FNC1,
+                                                                      21, 88, 88, 88, 88, 100, 24],),
+    # '(01)08720299927469(11)240621(17)250621(10)20240621/0001(21)xyz'
+    ('010872029992746911240621172506211020240621/0001' + FNC1_CHAR + '21xyz', [105, 102, 1, 8, 72, 2, 99, 92, 74, 69,
+                                                                               11, 24, 6, 21,
+                                                                               17, 25, 6, 21,
+                                                                               10, 20, 24, 6, 21, 100, 15, 99, 0, 1,
+                                                                               102, 21, 100, 88, 89, 90]),
+)
+@pytest.mark.parametrize('target, answer', CODE_BUILD_TEST)
+def test_code_build(target, answer):
+    gs1_128 = Gs1_128(target)
+    assert gs1_128._build() == answer