diff --git a/openapi_python_client/parser/properties/enum_property.py b/openapi_python_client/parser/properties/enum_property.py
index 0f0db0d61..49994e3da 100644
--- a/openapi_python_client/parser/properties/enum_property.py
+++ b/openapi_python_client/parser/properties/enum_property.py
@@ -187,7 +187,35 @@ def values_from_list(values: list[str] | list[int]) -> dict[str, ValueType]:
         """Convert a list of values into dict of {name: value}, where value can sometimes be None"""
         output: dict[str, ValueType] = {}
 
-        for i, value in enumerate(values):
+        # Strip out any duplicate values, while preserving the original order of the list.
+        # OpenAPI doesn't specifically disallow listing the exact same enum value twice; that
+        # would have no effect on validation behavior. The problem with it is just that we
+        # can't define two identically-named constants in the generated code. But there's no
+        # reason for us to do so, anyway; a single constant will suffice. So, just drop any
+        # duplicate value.
+        unique_values = []
+        for value in values:
+            if value not in unique_values:
+                unique_values.append(value)
+
+        # We normally would like to make nice-looking Python constant names for enum values,
+        # so that "myValue" becomes MY_VALUE, etc. However, that won't work if an enum has two
+        # values that differ only by case (which is allowed in OpenAPI).
+        use_case_sensitive_names = False
+        for i, value1 in enumerate(unique_values):
+            if use_case_sensitive_names:
+                break
+            for j, value2 in enumerate(unique_values):
+                if (
+                    i != j
+                    and isinstance(value1, str)
+                    and isinstance(value2, str)
+                    and value1.upper() == value2.upper()
+                ):
+                    use_case_sensitive_names = True
+                    break
+
+        for i, value in enumerate(unique_values):
             value = cast(Union[str, int], value)
             if isinstance(value, int):
                 if value < 0:
@@ -196,11 +224,14 @@ def values_from_list(values: list[str] | list[int]) -> dict[str, ValueType]:
                     output[f"VALUE_{value}"] = value
                 continue
             if value and value[0].isalpha():
-                key = value.upper()
+                key = value
             else:
                 key = f"VALUE_{i}"
             if key in output:
                 raise ValueError(f"Duplicate key {key} in Enum")
-            sanitized_key = utils.snake_case(key).upper()
+            if use_case_sensitive_names:
+                sanitized_key = utils.sanitize(key.replace(" ", "_"))
+            else:
+                sanitized_key = utils.snake_case(key.upper()).upper()
             output[sanitized_key] = utils.remove_string_escapes(value)
         return output
diff --git a/tests/test_parser/test_properties/test_init.py b/tests/test_parser/test_properties/test_init.py
index 3290dcd39..3d168eca3 100644
--- a/tests/test_parser/test_properties/test_init.py
+++ b/tests/test_parser/test_properties/test_init.py
@@ -364,14 +364,32 @@ def test_values_from_list(self):
             "VALUE_7": "",
         }
 
-    def test_values_from_list_duplicate(self):
+    def test_values_from_list_duplicate_is_skipped(self):
         from openapi_python_client.parser.properties import EnumProperty
 
         data = ["abc", "123", "a23", "abc"]
 
-        with pytest.raises(ValueError):
-            EnumProperty.values_from_list(data)
+        result = EnumProperty.values_from_list(data)
+
+        assert result == {
+            "ABC": "abc",
+            "VALUE_1": "123",
+            "A23": "a23",
+        }
 
+    def test_values_from_list_with_case_sensitive_names(self):
+        from openapi_python_client.parser.properties import EnumProperty
+
+        data = ["abc", "123", "ABC", "thing with spaces"]
+
+        result = EnumProperty.values_from_list(data)
+
+        assert result == {
+            "abc": "abc",
+            "VALUE_1": "123",
+            "ABC": "ABC",
+            "thing_with_spaces": "thing with spaces",
+        }
 
 class TestPropertyFromData:
     def test_property_from_data_str_enum(self, enum_property_factory, config):