diff --git a/pkg/apis/operator/v1alpha1/tektonconfig_types.go b/pkg/apis/operator/v1alpha1/tektonconfig_types.go
index a225e7132a..03f12ddc5a 100644
--- a/pkg/apis/operator/v1alpha1/tektonconfig_types.go
+++ b/pkg/apis/operator/v1alpha1/tektonconfig_types.go
@@ -59,7 +59,7 @@ type Prune struct {
 	Disabled bool `json:"disabled"`
 	// apply the prune job to the individual resources
 	// +optional
-	PrunePerResource bool `json:"prune-per-resource,omitempty"`
+	PrunePerResource bool `json:"prune-per-resource"`
 	// The resources which need to be pruned
 	Resources []string `json:"resources,omitempty"`
 	// The number of resource to keep
diff --git a/pkg/apis/operator/v1alpha1/tektonconfig_types_test.go b/pkg/apis/operator/v1alpha1/tektonconfig_types_test.go
new file mode 100644
index 0000000000..0043fc6161
--- /dev/null
+++ b/pkg/apis/operator/v1alpha1/tektonconfig_types_test.go
@@ -0,0 +1,49 @@
+/*
+Copyright 2026 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1alpha1
+
+import (
+	"encoding/json"
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+// TestPrune_PrunePerResourceJSONRoundTrip guards against the "prune-per-resource"
+// field being dropped when explicitly set to false. The admission webhook computes
+// a round-trip patch by marshaling a freshly unmarshaled copy of the request object
+// and diffing it against the original bytes; a `false` value on a field tagged
+// `omitempty` is indistinguishable from an unset field once marshaled, so the
+// webhook would emit a patch removing the key from the stored object.
+func TestPrune_PrunePerResourceJSONRoundTrip(t *testing.T) {
+	raw := []byte(`{"disabled":false,"prune-per-resource":false}`)
+
+	var p Prune
+	err := json.Unmarshal(raw, &p)
+	assert.NilError(t, err)
+	assert.Equal(t, p.PrunePerResource, false)
+
+	out, err := json.Marshal(p)
+	assert.NilError(t, err)
+
+	var roundTripped map[string]interface{}
+	err = json.Unmarshal(out, &roundTripped)
+	assert.NilError(t, err)
+
+	_, present := roundTripped["prune-per-resource"]
+	assert.Assert(t, present, "prune-per-resource key was dropped from marshaled JSON when false: %s", string(out))
+}