diff --git a/tests/ert/ui_tests/cli/analysis/test_design_matrix.py b/tests/ert/ui_tests/cli/analysis/test_design_matrix.py
index e75f1b10833..727451f2cfb 100644
--- a/tests/ert/ui_tests/cli/analysis/test_design_matrix.py
+++ b/tests/ert/ui_tests/cli/analysis/test_design_matrix.py
@@ -13,24 +13,30 @@
 from tests.ert.ui_tests.cli.run_cli import run_cli
 
 
+def _create_design_matrix(filename, design_sheet_df, default_sheet_df=None):
+    with pd.ExcelWriter(filename) as xl_write:
+        design_sheet_df.to_excel(xl_write, index=False, sheet_name="DesignSheet01")
+        if default_sheet_df is not None:
+            default_sheet_df.to_excel(
+                xl_write, index=False, sheet_name="DefaultSheet", header=False
+            )
+
+
 @pytest.mark.usefixtures("copy_poly_case")
 def test_run_poly_example_with_design_matrix():
-    design_matrix = "poly_design.xlsx"
     num_realizations = 10
     a_values = list(range(num_realizations))
-    design_matrix_df = pd.DataFrame(
-        {
-            "REAL": list(range(num_realizations)),
-            "a": a_values,
-            "category": 5 * ["cat1"] + 5 * ["cat2"],
-        }
+    _create_design_matrix(
+        "poly_design.xlsx",
+        pd.DataFrame(
+            {
+                "REAL": list(range(num_realizations)),
+                "a": a_values,
+                "category": 5 * ["cat1"] + 5 * ["cat2"],
+            }
+        ),
+        pd.DataFrame([["b", 1], ["c", 2]]),
     )
-    default_sheet_df = pd.DataFrame([["b", 1], ["c", 2]])
-    with pd.ExcelWriter(design_matrix) as xl_write:
-        design_matrix_df.to_excel(xl_write, index=False, sheet_name="DesignSheet01")
-        default_sheet_df.to_excel(
-            xl_write, index=False, sheet_name="DefaultSheet", header=False
-        )
 
     with open("poly.ert", "w", encoding="utf-8") as fout:
         fout.write(
@@ -105,21 +111,18 @@ def _evaluate(coeffs, x):
     ],
 )
 def test_run_poly_example_with_design_matrix_and_genkw_merge(default_values, error_msg):
-    design_matrix = "poly_design.xlsx"
     num_realizations = 10
     a_values = list(range(num_realizations))
-    design_matrix_df = pd.DataFrame(
-        {
-            "REAL": list(range(num_realizations)),
-            "a": a_values,
-        }
+    _create_design_matrix(
+        "poly_design.xlsx",
+        pd.DataFrame(
+            {
+                "REAL": list(range(num_realizations)),
+                "a": a_values,
+            }
+        ),
+        pd.DataFrame(default_values),
     )
-    default_sheet_df = pd.DataFrame(default_values)
-    with pd.ExcelWriter(design_matrix) as xl_write:
-        design_matrix_df.to_excel(xl_write, index=False, sheet_name="DesignSheet01")
-        default_sheet_df.to_excel(
-            xl_write, index=False, sheet_name="DefaultSheet", header=False
-        )
 
     with open("poly.ert", "w", encoding="utf-8") as fout:
         fout.write(
@@ -191,3 +194,92 @@ def _evaluate(coeffs, x):
         np.testing.assert_array_equal(params[:, 0], a_values)
         np.testing.assert_array_equal(params[:, 1], 10 * [1])
         np.testing.assert_array_equal(params[:, 2], 10 * [2])
+
+
+@pytest.mark.usefixtures("copy_poly_case")
+def test_run_poly_example_with_multiple_design_matrix_instances():
+    num_realizations = 10
+    a_values = list(range(num_realizations))
+    _create_design_matrix(
+        "poly_design_1.xlsx",
+        pd.DataFrame(
+            {
+                "REAL": list(range(num_realizations)),
+                "a": a_values,
+            }
+        ),
+        pd.DataFrame([["b", 1], ["c", 2]]),
+    )
+    _create_design_matrix(
+        "poly_design_2.xlsx",
+        pd.DataFrame(
+            {
+                "REAL": list(range(num_realizations)),
+                "d": num_realizations * [3],
+            }
+        ),
+        pd.DataFrame([["g", 4]]),
+    )
+
+    with open("poly.ert", "w", encoding="utf-8") as fout:
+        fout.write(
+            dedent(
+                """\
+                QUEUE_OPTION LOCAL MAX_RUNNING 10
+                RUNPATH poly_out/realization-<IENS>/iter-<ITER>
+                NUM_REALIZATIONS 10
+                MIN_REALIZATIONS 1
+                GEN_DATA POLY_RES RESULT_FILE:poly.out
+                DESIGN_MATRIX poly_design_1.xlsx DESIGN_SHEET:DesignSheet01 DEFAULT_SHEET:DefaultSheet
+                DESIGN_MATRIX poly_design_2.xlsx DESIGN_SHEET:DesignSheet01 DEFAULT_SHEET:DefaultSheet
+                INSTALL_JOB poly_eval POLY_EVAL
+                FORWARD_MODEL poly_eval
+                """
+            )
+        )
+
+    with open("poly_eval.py", "w", encoding="utf-8") as f:
+        f.write(
+            dedent(
+                """\
+                #!/usr/bin/env python
+                import json
+
+                def _load_coeffs(filename):
+                    with open(filename, encoding="utf-8") as f:
+                        return json.load(f)["DESIGN_MATRIX"]
+
+                def _evaluate(coeffs, x):
+                    return coeffs["a"] * x**2 + coeffs["b"] * x + coeffs["c"]
+
+                if __name__ == "__main__":
+                    coeffs = _load_coeffs("parameters.json")
+                    output = [_evaluate(coeffs, x) for x in range(10)]
+                    with open("poly.out", "w", encoding="utf-8") as f:
+                        f.write("\\n".join(map(str, output)))
+                """
+            )
+        )
+    os.chmod(
+        "poly_eval.py",
+        os.stat("poly_eval.py").st_mode | stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH,
+    )
+
+    run_cli(
+        ENSEMBLE_EXPERIMENT_MODE,
+        "--disable-monitor",
+        "poly.ert",
+        "--experiment-name",
+        "test-experiment",
+    )
+    storage_path = ErtConfig.from_file("poly.ert").ens_path
+    with open_storage(storage_path) as storage:
+        experiment = storage.get_experiment_by_name("test-experiment")
+        params = experiment.get_ensemble_by_name("default").load_parameters(
+            "DESIGN_MATRIX"
+        )["values"]
+        np.testing.assert_array_equal(params[:, 0], a_values)
+        np.testing.assert_array_equal(params[:, 1], 10 * [1])
+        np.testing.assert_array_equal(params[:, 2], 10 * [2])
+        np.testing.assert_array_equal(params[:, 3], 10 * [3])
+        np.testing.assert_array_equal(params[:, 4], 10 * [4])