diff --git a/asap-tools/experiments/recommended_sketch_configs/recommended_sketch_configs.py b/asap-tools/experiments/recommended_sketch_configs/recommended_sketch_configs.py
index d0ec7a87..a0b104e6 100644
--- a/asap-tools/experiments/recommended_sketch_configs/recommended_sketch_configs.py
+++ b/asap-tools/experiments/recommended_sketch_configs/recommended_sketch_configs.py
@@ -286,6 +286,16 @@ def generate(
         if not rows:
             skipped.append(f"{dataset}/{query_id}/{range_}: no recommendation")
             continue
+        # Experiment names carry no family, and sketch-bench emits one row per
+        # family per query kind, so a query id with both a keys and a values
+        # form has a CMS and a KLL row; the second would replace the first.
+        planner_rows = [r for r in rows if r["family"] in PLANNER_FAMILIES]
+        if len(planner_rows) > 1:
+            families = ", ".join(r["family"] for r in planner_rows)
+            raise ValueError(
+                f"{dataset}/{query_id}/{range_}: more than one planner family "
+                f"({families})"
+            )
         for row in rows:
             if row["family"] not in PLANNER_FAMILIES:
                 skipped.append(
diff --git a/asap-tools/experiments/tests/test_recommended_sketch_configs.py b/asap-tools/experiments/tests/test_recommended_sketch_configs.py
index 6b2b45ab..41ce2e92 100644
--- a/asap-tools/experiments/tests/test_recommended_sketch_configs.py
+++ b/asap-tools/experiments/tests/test_recommended_sketch_configs.py
@@ -177,6 +177,45 @@ def test_config_that_misses_target_is_skipped(self):
         self.assertEqual(configs, {})
         self.assertIn("does not meet the target", skipped[0])
 
+    def test_two_planner_families_for_one_query_raises(self):
+        # Experiment names carry no family, so the second row used to silently
+        # replace the first's config.
+        with self.assertRaisesRegex(ValueError, "google_2011/cpu_by_job_id/instant"):
+            rsc.generate(
+                [
+                    recommendation(
+                        "google_2011",
+                        "cpu_by_job_id",
+                        "instant",
+                        "cms",
+                        "rows=3 cols=4096",
+                    ),
+                    recommendation(
+                        "google_2011", "cpu_by_job_id", "instant", "kll", "k=200"
+                    ),
+                ],
+                [("google_2011", "cpu_by_job_id", "instant")],
+                "/traces",
+            )
+
+    def test_two_planner_families_for_unselected_query_are_ignored(self):
+        # rt_p99_by_msname has keys and values forms, so sketch-bench emits CMS
+        # and KLL rows for it; that must not block the selected queries.
+        configs, _ = rsc.generate(
+            self.recommendations
+            + [
+                recommendation(
+                    "alibaba_v2022", "rt_p99_by_msname", "5m", "cms", "rows=3 cols=4096"
+                ),
+                recommendation(
+                    "alibaba_v2022", "rt_p99_by_msname", "5m", "kll", "k=200"
+                ),
+            ],
+            [("google_2011", "cpu_by_job_id", "5m")],
+            "/traces",
+        )
+        self.assertEqual(len(configs), 2)
+
 
 class ComposeGeneratedConfigTest(unittest.TestCase):
     def test_recommended_config_overrides_config_yaml_sketch_parameters(self):