diff --git a/src/ert/config/design_matrix.py b/src/ert/config/design_matrix.py
index e4fb4c6ff8f..cf3cb9fde99 100644
--- a/src/ert/config/design_matrix.py
+++ b/src/ert/config/design_matrix.py
@@ -77,9 +77,6 @@ def from_config_list(cls, config_list: List[str]) -> "DesignMatrix":
     def read_design_matrix(
         self,
     ) -> None:
-        """
-        Reads out all file content from different files and create dataframes
-        """
         param_names = (
             pd.read_excel(
                 self.xls_filename,
@@ -91,11 +88,13 @@ def read_design_matrix(
             .iloc[0]
             .apply(lambda x: x.strip() if isinstance(x, str) else x)
         )
-        if len(param_names) - len(set(param_names)) != 0:
-            raise ValueError("Duplicate parameter names found in design sheet")
         design_matrix_df = DesignMatrix._read_excel(
-            self.xls_filename, self.design_sheet
-        ).rename(columns=lambda x: str(x).strip())
+            self.xls_filename,
+            self.design_sheet,
+            header=None,
+            skiprows=1,
+        )
+        design_matrix_df.columns = param_names
 
         if "REAL" in design_matrix_df.columns:
             if not is_integer_dtype(design_matrix_df.dtypes["REAL"]) or any(
@@ -152,6 +151,7 @@ def _read_excel(
         sheet_name: str,
         usecols: Optional[Union[int, List[int]]] = None,
         header: Optional[int] = 0,
+        skiprows: Optional[int] = None,
         dtype: Optional[str] = None,
     ) -> pd.DataFrame:
         """
@@ -165,30 +165,30 @@ def _read_excel(
             sheet_name,
             usecols=usecols,
             header=header,
+            skiprows=skiprows,
             dtype=dtype,
         )
         return dframe.dropna(axis=1, how="all")
 
+    @staticmethod
     def _validate_design_matrix(design_matrix: pd.DataFrame) -> List[str]:
         """
-        Validate header in user inputted design matrix
-        :raises: ValueError if design matrix contains empty headers
+        Validate user inputted design matrix
+        :raises: ValueError if design matrix contains empty headers or empty cells
         """
         if design_matrix.empty:
             return []
         errors = []
+        column_na_mask = design_matrix.columns.isna()
         column_indexes_unnamed = [
-            index
-            for index, value in enumerate(
-                design_matrix.columns.str.contains("^Unnamed")
-            )
-            if value
+            index for index, value in enumerate(column_na_mask) if value
         ]
         if len(column_indexes_unnamed) > 0:
             errors.append(
                 f"Column headers not present in column {column_indexes_unnamed}"
             )
-
+        if not design_matrix.columns[~column_na_mask].is_unique:
+            errors.append("Duplicate parameter names found in design sheet")
         empties = [
             f"Realization {design_matrix.index[i]}, column {design_matrix.columns[j]}"
             for i, j in zip(*np.where(pd.isna(design_matrix)))
@@ -202,7 +202,7 @@ def _read_defaultssheet(
         xls_filename: Union[Path, str], defaults_sheetname: str
     ) -> Dict[str, Union[str, float]]:
         """
-        Construct a dataframe of keys and values to be used as defaults from the
+        Construct a dict of keys and values to be used as defaults from the
         first two columns in a spreadsheet.
 
         Returns a dict of default values