diff --git a/validphys2/src/validphys/lhio.py b/validphys2/src/validphys/lhio.py
index ebe2f3d671..6aaf2a0bf0 100644
--- a/validphys2/src/validphys/lhio.py
+++ b/validphys2/src/validphys/lhio.py
@@ -310,8 +310,8 @@ def hessian_from_lincomb(pdf, V, set_name=None, folder = None, extra_fields=None
                 out.write(f"SetDesc: \"Hessian {pdf}_hessian\"\n")
             elif l.find("NumMembers:") >= 0:
                 out.write(f"NumMembers: {neig+1}\n")
-            elif l.find("error_type: replicas") >= 0:
-                out.write("error_type: symmhessian\n")
+            elif l.find("ErrorType: replicas") >= 0:
+                out.write("ErrorType: symmhessian\n")
             else:
                 out.write(l)
         if extra_fields is not None:
diff --git a/validphys2/src/validphys/tests/test_mc2hessian.py b/validphys2/src/validphys/tests/test_mc2hessian.py
new file mode 100644
index 0000000000..51b1e4ec2c
--- /dev/null
+++ b/validphys2/src/validphys/tests/test_mc2hessian.py
@@ -0,0 +1,54 @@
+"""
+    Test for the mc2hessian module
+"""
+import contextlib
+import lhapdf
+from validphys.api import API
+
+NEIG = 5
+
+
+@contextlib.contextmanager
+def temp_lhapdf_path(folder):
+    """Modify the data path for LHAPDF sets"""
+    oldpaths = lhapdf.paths()
+    lhapdf.setPaths([str(folder)])
+    try:
+        yield
+    finally:
+        lhapdf.setPaths(oldpaths)
+
+
+def test_mc2hessian(data_config, tmp):
+    """Tests that the generated hessian PDF is indeed marked as such
+    and that the metadata is not obviously broken
+    """
+    config = dict(data_config)
+    pdf_hessian_name = f"{config['pdf']}_hessian_{NEIG}"
+
+    config["Neig"] = NEIG
+    config["output_path"] = tmp
+    API.mc2hessian(**config)
+
+    # Save a reference to the original pdf
+    orig_pdf_info = API.pdf(pdf=config["pdf"]).info
+
+    # Now try to read the PDF we just wrote to some non_std location
+    with temp_lhapdf_path(tmp.as_posix()):
+        pdf = API.pdf(pdf=pdf_hessian_name)
+
+        # Check the correct changed metadata
+        assert pdf.error_type == "symmhessian"
+        assert len(pdf) == NEIG + 1
+
+        # Now check that all info is the same as the original
+        # except for ErrorType that _must_ be different
+        skip_this = ["SetDesc", "NumMembers"]
+        for key, item in orig_pdf_info.items():
+            if key in skip_this:
+                continue
+            new_item = pdf.info[key]
+            if key == "ErrorType":
+                assert item != new_item
+            else:
+                assert item == new_item