diff --git a/dzonegit.py b/dzonegit.py
index bbca859..9e6b371 100644
--- a/dzonegit.py
+++ b/dzonegit.py
@@ -14,6 +14,9 @@ from pathlib import Path
 from string import Template
 
 
+SERIAL_SMUDGE_TAG = "DZONEGIT_DO_NOT_CHANGE_OLD_SERIAL_"
+
+
 class HookException(ValueError):
     """Exception raised when there is an error in input data.
 
@@ -493,3 +496,32 @@ def post_receive(stdin=sys.stdin):
                     cmd.append(z)
                     print("Calling {}…".format(" ".join(cmd)))
                     subprocess.run(cmd)
+
+
+def clean_serial(stdin=sys.stdin):
+    """ Git filter command to replace smudged serial with an increased one. """
+    for line in stdin:
+        m = re.search(
+            r"(\s){}([0-9]+)(\s)".format(SERIAL_SMUDGE_TAG),
+            line,
+        )
+        if m:
+            oldserial = m.group(2)
+            newserial = get_increased_serial(oldserial)
+            line = line.replace(SERIAL_SMUDGE_TAG + oldserial, newserial)
+        print(line, end="")
+
+
+def smudge_serial(stdin=sys.stdin):
+    """ Git filter command to smudge SOA serial number. """
+    sys.stderr.write("Smudging {}…\n".format(sys.argv))
+    zonedata = stdin.read()
+    if SERIAL_SMUDGE_TAG not in zonedata:
+        zonedata = re.sub(
+            r'(^.*\sSOA\s.+?\s)([0-9]+[^0-9])',
+            r'\g<1>{}\g<2>'.format(SERIAL_SMUDGE_TAG),
+            zonedata,
+            count=1,
+            flags=re.DOTALL | re.IGNORECASE | re.MULTILINE,
+        )
+    print(zonedata, end="")
diff --git a/setup.py b/setup.py
index 30802cf..1af417e 100644
--- a/setup.py
+++ b/setup.py
@@ -23,6 +23,8 @@ setup(
                 "dzonegit-pre-receive = dzonegit:pre_receive",
                 "dzonegit-post-receive = dzonegit:post_receive",
                 "dzonegit-update = dzonegit:update",
+                "dzonegit-smudge-serial = dzonegit:smudge_serial",
+                "dzonegit-clean-serial = dzonegit:clean_serial",
             ],
     },
     classifiers=[
diff --git a/test_dzonegit.py b/test_dzonegit.py
index ffb7d17..156aace 100644
--- a/test_dzonegit.py
+++ b/test_dzonegit.py
@@ -332,3 +332,42 @@ def test_get_zone_wildcards():
         "a.long.zone.name", "*.long.zone.name",
         "*.zone.name", "*.name", "*",
     ]
+
+
+def test_smudge_serial(capsys):
+    stdin = StringIO("""
+@ 60 IN SOA ns hm (
+                60 ; serial
+                60 ; refresh
+                60 ; retry
+                60 ; expire
+                60 ; minimum
+                )
+  60 NS ns.example.org.
+""")
+    dzonegit.smudge_serial(stdin)
+    stdout = capsys.readouterr().out
+
+    assert "{}60 ; serial".format(dzonegit.SERIAL_SMUDGE_TAG) in stdout
+    stdin = StringIO(stdout)
+    dzonegit.smudge_serial(stdin)
+    assert stdout == capsys.readouterr().out
+
+
+def test_clean_serial(capsys):
+    stdin = StringIO("""
+@ 60 IN SOA ns hm (
+                {}60 ; serial
+                60 ; refresh
+                60 ; retry
+                60 ; expire
+                60 ; minimum
+                )
+  60 NS ns.example.org.
+""".format(dzonegit.SERIAL_SMUDGE_TAG))
+    dzonegit.clean_serial(stdin)
+    stdout = capsys.readouterr().out
+    assert " 61 ; serial" in stdout
+    stdin = StringIO(stdout)
+    dzonegit.clean_serial(stdin)
+    assert stdout == capsys.readouterr().out