diff --git a/src/ert/config/design_matrix.py b/src/ert/config/design_matrix.py
index c05790a3ffb..4e8ed2c7fa2 100644
--- a/src/ert/config/design_matrix.py
+++ b/src/ert/config/design_matrix.py
@@ -97,7 +97,6 @@ def read_design_matrix(
 
         # ignoring errors here is deprecated in pandas, should find another solution
         # design_matrix_sheet = design_matrix_sheet.apply(pd.to_numeric, errors="ignore")
-        parameter_configuration = {}
         transform_function_definitions: list[TransformFunctionDefinition] = []
         for parameter in design_matrix_df.columns:
             transform_function_definitions.append(
@@ -107,14 +106,16 @@ def read_design_matrix(
                     values=[],
                 )
             )
-        parameter_configuration[DESIGN_MATRIX_GROUP] = GenKwConfig(
-            name=DESIGN_MATRIX_GROUP,
-            forward_init=False,
-            template_file=None,
-            output_file=None,
-            transform_function_definitions=transform_function_definitions,
-            update=False,
-        )
+        parameter_configuration = [
+            GenKwConfig(
+                name=DESIGN_MATRIX_GROUP,
+                forward_init=False,
+                template_file=None,
+                output_file=None,
+                transform_function_definitions=transform_function_definitions,
+                update=False,
+            )
+        ]
 
         design_matrix_df.columns = pd.MultiIndex.from_product(
             [[DESIGN_MATRIX_GROUP], design_matrix_df.columns]