diff --git a/docs/release-notes/9966-fix-grid.rst b/docs/release-notes/9966-fix-grid.rst
new file mode 100644
index 00000000000..f36dc1b8dc6
--- /dev/null
+++ b/docs/release-notes/9966-fix-grid.rst
@@ -0,0 +1,7 @@
+:orphan:
+
+**Fixes**
+
+-  Previously, during a grid search, if a hyperparameter contained an empty nested hyperparameter
+   (that is, just an empty map), that hyperparameter would not appear in the hparams passed to the
+   trial.
diff --git a/master/pkg/searcher/grid.go b/master/pkg/searcher/grid.go
index 2e6e512648f..a83c9cc6e03 100644
--- a/master/pkg/searcher/grid.go
+++ b/master/pkg/searcher/grid.go
@@ -260,8 +260,13 @@ func getGridAxes(route []string, h expconf.Hyperparameter) []gridAxis {
 		return []gridAxis{axis}
 	case h.RawNestedHyperparameter != nil:
 		axes := []gridAxis{}
-		// Use h.Each for deterministic ordering.
 		nested := expconf.Hyperparameters(*h.RawNestedHyperparameter)
+		// Make sure empty maps don't disappear after sampling.
+		if len(nested) == 0 {
+			axes = append(axes, gridAxis{axisValue{route, map[string]interface{}{}}})
+			return axes
+		}
+		// Use h.Each for deterministic ordering.
 		nested.Each(func(name string, subparam expconf.HyperparameterV0) {
 			// make a completely clean copy of route
 			var subroute []string
diff --git a/master/pkg/searcher/grid_test.go b/master/pkg/searcher/grid_test.go
index b81ca83e371..cffb52f314d 100644
--- a/master/pkg/searcher/grid_test.go
+++ b/master/pkg/searcher/grid_test.go
@@ -74,6 +74,20 @@ func TestHyperparameterGridMethod(t *testing.T) {
 		len(getGridAxes([]string{"x"}, expconf.Hyperparameter{RawConstHyperparameter: &constParam})[0]),
 		1,
 	)
+	// Regression test: make sure empty nested hyperparameters don't disappear during sampling.
+	nestedParam := map[string]expconf.Hyperparameter{
+		"empty": {RawNestedHyperparameter: &map[string]expconf.Hyperparameter{}},
+		"full":  {RawCategoricalHyperparameter: &catParam},
+	}
+	result := getGridAxes([]string{"x"}, expconf.Hyperparameter{RawNestedHyperparameter: &nestedParam})
+	assert.DeepEqual(t, result, []gridAxis{
+		[]axisValue{{Route: []string{"x", "empty"}, Value: map[string]interface{}{}}},
+		[]axisValue{
+			{Route: []string{"x", "full"}, Value: 1},
+			{Route: []string{"x", "full"}, Value: 2},
+			{Route: []string{"x", "full"}, Value: 3},
+		},
+	})
 }
 
 func TestGrid(t *testing.T) {