diff --git a/home/import_helpers.py b/home/import_helpers.py
index 7a2e80b5..3a4cf307 100644
--- a/home/import_helpers.py
+++ b/home/import_helpers.py
@@ -1,6 +1,6 @@
 # The error messages are processed and parsed into a list of messages we return to the user
 import csv
-from collections.abc import Generator, Iterator
+from collections.abc import Iterator
 from datetime import datetime
 from io import BytesIO, StringIO
 from typing import Any
@@ -165,21 +165,27 @@ def extract_errors(data: dict[str | int, Any] | list[str]) -> dict[str, str]:
     return error_message
 
 
-def fix_rows(
-    rows: Generator[dict[str, str], None, None] | Iterator[dict[str | Any, Any]]
-) -> Iterator[dict[str, str | None]]:
+def fix_rows(rows: Iterator[dict[str | Any, Any]]) -> Iterator[dict[str, str | None]]:
     """
     Fix keys for all rows by lowercasing keys and removing whitespace from keys and values
     """
-    for row in rows:
-        yield fix_row(row)
+    for index, row in enumerate(rows):
+        yield fix_row(row, index)
 
 
-def fix_row(row: dict[str, str]) -> dict[str, str | None]:
+def fix_row(row: dict[str, str | None], index: int) -> dict[str, str | None]:
     """
     Fix a single row by lowercasing the key and removing whitespace from the key and value
     """
     try:
+        if index == 0:
+            keys = [_normalise_key(k) for k, v in row.items()]
+            if len(keys) != len(set(keys)):
+                raise ImportException(
+                    "Invalid format. Please check that there are no duplicate headers.",
+                    row_num=index,
+                )
+
         return {_normalise_key(k): _normalise_value(v) for k, v in row.items()}
     except AttributeError:
         raise ImportException(
@@ -204,11 +210,11 @@ def parse_file(
     return enumerate(fix_rows(read_rows(file_content)), start=2)
 
 
-def read_csv(file_content: bytes) -> Iterator[dict[str, str | None]]:
+def read_csv(file_content: bytes) -> Iterator[dict[str, Any]]:
     return csv.DictReader(StringIO(file_content.decode()))
 
 
-def read_xlsx(file_content: bytes) -> Generator[dict[str, Any], None, None]:
+def read_xlsx(file_content: bytes) -> Iterator[dict[str, Any]]:
     workbook = load_workbook(BytesIO(file_content), read_only=True, data_only=True)
     worksheet = get_active_sheet(workbook)
 
diff --git a/home/tests/test_assessment_import_export.py b/home/tests/test_assessment_import_export.py
index 2a5fce7e..b5210833 100644
--- a/home/tests/test_assessment_import_export.py
+++ b/home/tests/test_assessment_import_export.py
@@ -560,7 +560,7 @@ def test_extra_columns_xlsx(
             csv_impexp.import_content_file("assessment_results.csv", purge=False)
             xlsx_impexp.import_file("extra_columns.xlsx")
         assert e.value.message == [
-            "Invalid format. Please check that all row values " "have headers."
+            "Invalid format. Please check that all row values have headers."
         ]
 
     def test_mismatched_length_answers(self, csv_impexp: ImportExport) -> None:
diff --git a/home/tests/test_content_import_export.py b/home/tests/test_content_import_export.py
index d288ed39..5e038fb9 100644
--- a/home/tests/test_content_import_export.py
+++ b/home/tests/test_content_import_export.py
@@ -1436,6 +1436,28 @@ def test_import_ordered_sets_csv(self, csv_impexp: ImportExport) -> None:
             ("relationship", "in_a_relationship"),
         ]
 
+    def test_import_ordered_sets_duplicate_header_csv(
+        self, csv_impexp: ImportExport
+    ) -> None:
+        """
+        Importing a CSV with duplicate headers should throw an error
+        """
+        set_profile_field_options()
+        pt, _created = Locale.objects.get_or_create(language_code="pt")
+        HomePage.add_root(locale=pt, title="Home (pt)", slug="home-pt")
+
+        csv_impexp.import_file("contentpage_required_fields_multi_locale.csv")
+        content = csv_impexp.read_bytes("ordered_content_duplicate_header.csv")
+
+        with pytest.raises(ImportException) as e:
+            csv_impexp.import_ordered_sets(content)
+
+        assert e.value.row_num == 0
+
+        assert e.value.message == [
+            "Invalid format. Please check that there are no duplicate headers."
+        ]
+
     def test_import_ordered_sets_no_profile_fields_csv(
         self, csv_impexp: ImportExport
     ) -> None: