diff --git a/internal/controller/overrides.go b/internal/controller/overrides.go
index cb3d325c..6244fdd0 100644
--- a/internal/controller/overrides.go
+++ b/internal/controller/overrides.go
@@ -138,8 +138,25 @@ func mergeAffinity(base, patch *corev1.Affinity) *corev1.Affinity {
 // t is treated as read-only; it is only marshaled, never written to.
 // VolumeMounts are handled separately to allow multiple mounts at the same path; handled by ProjectVolumes.
 func ApplyContainerTemplateOverrides(container *corev1.Container, t *v1.ContainerTemplateSpec) (corev1.Container, error) {
+	base := container
+
+	// Strategic merge patch deep-merges corev1.Capabilities field-by-field; the schema
+	// has no patchStrategy=replace directive on Capabilities. A user setting only
+	// Drop:[ALL] would otherwise leave the operator-defaulted Add list in place,
+	// producing a spec rejected by `restricted` PodSecurity. Treat user-provided
+	// Capabilities as authoritative for the whole sub-struct by clearing it on the
+	// base before SMP. Other SecurityContext fields still deep-merge as expected.
+	if t.SecurityContext != nil && t.SecurityContext.Capabilities != nil &&
+		base.SecurityContext != nil && base.SecurityContext.Capabilities != nil {
+		baseCopy := *base
+		scCopy := *base.SecurityContext
+		scCopy.Capabilities = nil
+		baseCopy.SecurityContext = &scCopy
+		base = &baseCopy
+	}
+
 	patchContainer := corev1.Container{
-		Name:            container.Name,
+		Name:            base.Name,
 		Image:           t.Image.String(),
 		ImagePullPolicy: t.ImagePullPolicy,
 		Resources:       t.Resources,
@@ -150,7 +167,7 @@ func ApplyContainerTemplateOverrides(container *corev1.Container, t *v1.Containe
 		// ReadinessProbe is handled manually
 	}
 
-	mergedContainer, err := patchResource(container, patchContainer, containerSchema)
+	mergedContainer, err := patchResource(base, patchContainer, containerSchema)
 	if err != nil {
 		return corev1.Container{}, fmt.Errorf("patch container: %w", err)
 	}
diff --git a/internal/controller/overrides_test.go b/internal/controller/overrides_test.go
index a9e19fcb..23625e5c 100644
--- a/internal/controller/overrides_test.go
+++ b/internal/controller/overrides_test.go
@@ -101,6 +101,116 @@ var _ = Describe("ApplyContainerTemplateOverrides", func() {
 			Expect(container.SecurityContext.RunAsUser).NotTo(BeNil())
 			Expect(*container.SecurityContext.RunAsUser).To(Equal(int64(1000)), "user RunAsUser should be applied")
 		})
+
+		Describe("Capabilities", func() {
+			// Strategic merge patch deep-merges corev1.Capabilities field-by-field,
+			// so a user setting only Drop:[ALL] would otherwise leave the operator's
+			// defaulted Add list in place — producing a spec rejected by `restricted`
+			// PodSecurity. The merge must treat user-provided Capabilities as
+			// authoritative for the whole sub-struct.
+			// See https://github.com/ClickHouse/clickhouse-operator/issues/174.
+			It("should let user Drop:[ALL] override operator-defaulted Add", func() {
+				container, err := ApplyContainerTemplateOverrides(
+					&corev1.Container{
+						Name: "server",
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Add: []corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"},
+							},
+						},
+					},
+					&v1.ContainerTemplateSpec{
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Drop: []corev1.Capability{"ALL"},
+							},
+						},
+					},
+				)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(container.SecurityContext).NotTo(BeNil())
+				Expect(container.SecurityContext.Capabilities).NotTo(BeNil())
+				Expect(container.SecurityContext.Capabilities.Drop).To(Equal([]corev1.Capability{"ALL"}))
+				Expect(container.SecurityContext.Capabilities.Add).To(BeEmpty(),
+					"operator-defaulted Add must not survive when the user sets Drop:[ALL]")
+			})
+
+			It("should let user-set Add replace operator-defaulted Add", func() {
+				container, err := ApplyContainerTemplateOverrides(
+					&corev1.Container{
+						Name: "server",
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Add: []corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"},
+							},
+						},
+					},
+					&v1.ContainerTemplateSpec{
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Add: []corev1.Capability{"NET_BIND_SERVICE"},
+							},
+						},
+					},
+				)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(container.SecurityContext.Capabilities).NotTo(BeNil())
+				Expect(container.SecurityContext.Capabilities.Add).To(Equal([]corev1.Capability{"NET_BIND_SERVICE"}),
+					"user Add list should replace, not merge with, operator defaults")
+			})
+
+			It("should preserve operator capabilities when user SecurityContext omits Capabilities", func() {
+				container, err := ApplyContainerTemplateOverrides(
+					&corev1.Container{
+						Name: "server",
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Add: []corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"},
+							},
+						},
+					},
+					&v1.ContainerTemplateSpec{
+						SecurityContext: &corev1.SecurityContext{
+							RunAsNonRoot: new(true),
+						},
+					},
+				)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(container.SecurityContext.Capabilities).NotTo(BeNil())
+				Expect(container.SecurityContext.Capabilities.Add).To(Equal(
+					[]corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"}),
+					"operator capabilities must survive when the user does not set capabilities")
+				Expect(container.SecurityContext.RunAsNonRoot).NotTo(BeNil())
+				Expect(*container.SecurityContext.RunAsNonRoot).To(BeTrue())
+			})
+
+			It("should not mutate the caller's container or its SecurityContext", func() {
+				baseCaps := &corev1.Capabilities{
+					Add: []corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"},
+				}
+				baseSC := &corev1.SecurityContext{Capabilities: baseCaps}
+				base := &corev1.Container{Name: "server", SecurityContext: baseSC}
+
+				_, err := ApplyContainerTemplateOverrides(
+					base,
+					&v1.ContainerTemplateSpec{
+						SecurityContext: &corev1.SecurityContext{
+							Capabilities: &corev1.Capabilities{
+								Drop: []corev1.Capability{"ALL"},
+							},
+						},
+					},
+				)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(base.SecurityContext).To(BeIdenticalTo(baseSC), "caller's SecurityContext pointer should be untouched")
+				Expect(baseSC.Capabilities).To(BeIdenticalTo(baseCaps), "caller's Capabilities pointer should be untouched")
+				Expect(baseCaps.Add).To(Equal([]corev1.Capability{"IPC_LOCK", "PERFMON", "SYS_PTRACE"}))
+			})
+		})
 	})
 
 	Describe("Probes", func() {