diff --git a/ocrd_calamari/fix_calamari1_model.py b/ocrd_calamari/fix_calamari1_model.py
new file mode 100644
index 0000000..96f880f
--- /dev/null
+++ b/ocrd_calamari/fix_calamari1_model.py
@@ -0,0 +1,39 @@
+import re
+import json
+import click
+from glob import glob
+from copy import deepcopy
+
+from ocrd_calamari.util import working_directory
+
+@click.command
+@click.argument('checkpoint_dir')
+def fix_calamari1_model(checkpoint_dir):
+    """
+    Fix old Calamari 1 models.
+
+    This currently means fixing regexen in "replacements" to have their global flags
+    in front of the rest of the regex.
+    """
+    with working_directory(checkpoint_dir):
+        for fn in glob("*.json"):
+            with open(fn, "r") as fp:
+                j = json.load(fp)
+                old_j = deepcopy(j)
+
+            for v in j["model"].values():
+                if type(v) != dict:
+                    continue
+                for child in v.get("children", []):
+                    for replacement in child.get("replacements", []):
+                        # Move global flags in front
+                        replacement["old"] = re.sub(
+                            r"^(.*)\(\?u\)$", r"(?u)\1", replacement["old"]
+                        )
+
+            if j == old_j:
+                print(f"{fn} unchanged.")
+            else:
+                with open(fn, "w") as fp:
+                    json.dump(j, fp, indent=2)
+                print(f"{fn} fixed.")
diff --git a/ocrd_calamari/util.py b/ocrd_calamari/util.py
new file mode 100644
index 0000000..343f175
--- /dev/null
+++ b/ocrd_calamari/util.py
@@ -0,0 +1,14 @@
+import os
+
+class working_directory:
+    """Context manager to temporarily change the working directory"""
+
+    def __init__(self, wd):
+        self.wd = wd
+
+    def __enter__(self):
+        self.old_wd = os.getcwd()
+        os.chdir(self.wd)
+
+    def __exit__(self, etype, value, traceback):
+        os.chdir(self.old_wd)
diff --git a/setup.py b/setup.py
index db1926d..e9036bc 100644
--- a/setup.py
+++ b/setup.py
@@ -25,6 +25,7 @@ setup(
     entry_points={
         'console_scripts': [
             'ocrd-calamari-recognize=ocrd_calamari.cli:ocrd_calamari_recognize',
+            'fix-calamari1-model=ocrd_calamari.fix_calamari1_model:fix_calamari1_model',
         ]
     },
 )