diff --git a/tests/testthat/test-validate_config.R b/tests/testthat/test-validate_config.R
index e1d8420..ad346c3 100644
--- a/tests/testthat/test-validate_config.R
+++ b/tests/testthat/test-validate_config.R
@@ -251,3 +251,22 @@ test_that("v4 validation works", {
     )
   )
 })
+
+test_that("target keys with 2 properties throws error", {
+  skip_if_offline()
+  config_path <- testthat::test_path("testdata", "v4.0.1-tasks-2-target_keys.json")
+  out <- suppressMessages(
+    validate_config(
+      config_path = config_path,
+      # TDOD: remove branch argument when v4.0.1 is released.
+      branch = "ak/v4.0.1/restrict-target-key-value-pair-n/117"
+    )
+  )
+  expect_false(out)
+
+  expect_equal(
+    unique(attr(out, "errors")$message),
+    "must NOT have more than 1 items"
+  )
+  expect_equal(nrow(attr(out, "errors")), 2L)
+})
diff --git a/tests/testthat/testdata/v4.0.1-tasks-2-target_keys.json b/tests/testthat/testdata/v4.0.1-tasks-2-target_keys.json
new file mode 100644
index 0000000..d9a8c81
--- /dev/null
+++ b/tests/testthat/testdata/v4.0.1-tasks-2-target_keys.json
@@ -0,0 +1,164 @@
+{
+    "schema_version": "https://raw.githubusercontent.com/hubverse-org/schemas/main/v4.0.1/tasks-schema.json",
+    "rounds": [{
+            "round_id_from_variable": true,
+            "round_id": "forecast_date",
+            "model_tasks": [{
+                "task_ids": {
+                    "forecast_date": {
+                        "required": null,
+                        "optional": [
+                            "2022-12-12", "2022-12-19", "2022-12-26", "2023-01-02", "2023-01-09",
+                            "2023-01-16", "2023-01-23", "2023-01-30", "2023-02-06", "2023-02-13",
+                            "2023-02-20", "2023-02-27", "2023-03-06", "2023-03-13", "2023-03-20",
+                            "2023-03-27", "2023-04-03", "2023-04-10", "2023-04-17", "2023-04-24",
+                            "2023-05-01"
+                        ]
+                    },
+                    "target": {
+                        "required": null,
+                        "optional": ["wk ahead inc"]
+                    },
+                    "target_metric": {
+                        "required": null,
+                        "optional": ["flu hosp"]
+                    },
+                    "horizon": {
+                        "required": [2],
+                        "optional": [1]
+                    },
+                    "location": {
+                        "required": ["US"],
+                        "optional": [
+                            "01",
+                            "02"
+                        ]
+                    },
+                    "target_date": {
+                        "required": null,
+                        "optional": [
+                            "2022-12-19", "2022-12-26", "2023-01-02", "2023-01-09",
+                            "2023-01-16", "2023-01-23", "2023-01-30", "2023-02-06", "2023-02-13",
+                            "2023-02-20", "2023-02-27", "2023-03-06", "2023-03-13", "2023-03-20",
+                            "2023-03-27", "2023-04-03", "2023-04-10", "2023-04-17", "2023-04-24",
+                            "2023-05-01", "2023-05-08", "2023-05-15"
+                        ]
+                    }
+                },
+                "output_type": {
+                    "sample": {
+                        "output_type_id_params": {
+                            "type": "character",
+                            "min_samples_per_task": 50,
+                            "max_samples_per_task": 100,
+                            "max_length": 10
+                        },
+                        "is_required": true,
+                        "value": {
+                            "type": "integer",
+                            "minimum": 0
+                        }
+                    },
+                    "mean": {
+                        "output_type_id": {
+                            "required": null
+                        },
+                        "is_required": true,
+                        "value": {
+                            "type": "double",
+                            "minimum": 0
+                        }
+                    }
+                },
+                "target_metadata": [{
+                    "target_id": "wk ahead inc flu hosp",
+                    "target_name": "weekly influenza hospitalization incidence",
+                    "target_units": "rate per 100,000 population",
+                    "target_keys": {
+                        "target": "wk ahead inc",
+                        "target_metric": "flu hosp"
+                    },
+                    "target_type": "discrete",
+                    "description": "This target represents the counts of new hospitalizations per horizon week.",
+                    "is_step_ahead": true,
+                    "time_unit": "week"
+                }]
+            }, {
+                "task_ids": {
+                    "forecast_date": {
+                        "required": null,
+                        "optional": [
+                            "2022-12-12", "2022-12-19", "2022-12-26", "2023-01-02", "2023-01-09",
+                            "2023-01-16", "2023-01-23", "2023-01-30", "2023-02-06", "2023-02-13",
+                            "2023-02-20", "2023-02-27", "2023-03-06", "2023-03-13", "2023-03-20",
+                            "2023-03-27", "2023-04-03", "2023-04-10", "2023-04-17", "2023-04-24",
+                            "2023-05-01"
+                        ]
+                    },
+                    "target": {
+                        "required": null,
+                        "optional": ["wk flu hosp"]
+                    },
+                    "target_metric": {
+                        "required": null,
+                        "optional": ["rate change"]
+                    },
+                    "horizon": {
+                        "required": [2],
+                        "optional": [1]
+                    },
+                    "location": {
+                        "required": ["US"],
+                        "optional": [
+                            "01",
+                            "02"
+                        ]
+                    },
+                    "target_date": {
+                        "required": null,
+                        "optional": [
+                            "2022-12-19", "2022-12-26", "2023-01-02", "2023-01-09",
+                            "2023-01-16", "2023-01-23", "2023-01-30", "2023-02-06", "2023-02-13",
+                            "2023-02-20", "2023-02-27", "2023-03-06", "2023-03-13", "2023-03-20",
+                            "2023-03-27", "2023-04-03", "2023-04-10", "2023-04-17", "2023-04-24",
+                            "2023-05-01", "2023-05-08", "2023-05-15"
+                        ]
+                    }
+                },
+                "output_type": {
+                    "pmf": {
+                        "output_type_id": {
+                            "required": ["large_decrease", "decrease", "stable", "increase", "large_increase"]
+                        },
+                        "is_required": false,
+                        "value": {
+                            "type": "double",
+                            "minimum": 0,
+                            "maximum": 1
+                        }
+                    }
+                },
+                "target_metadata": [{
+                    "target_id": "wk flu hosp rate change",
+                    "target_name": "weekly influenza hospitalization rate change",
+                    "target_units": "rate per 100,000 population",
+                    "target_keys": {
+                        "target": "wk flu hosp",
+                        "target_metric": "rate change"
+                    },
+                    "target_type": "nominal",
+                    "description": "This target represents the change in the rate of new hospitalizations per week comparing the week ending two days prior to the forecast_date to the week ending h weeks after the forecast_date.",
+                    "is_step_ahead": true,
+                    "time_unit": "week"
+                }]
+            }],
+            "submissions_due": {
+                "relative_to": "forecast_date",
+                "start": -6,
+                "end": 2
+            },
+            "derived_task_ids": ["target_date"]
+        }
+
+    ]
+}