diff --git a/pkg/smartcontract/manifest/abi.go b/pkg/smartcontract/manifest/abi.go
index 15211919e..67e28b073 100644
--- a/pkg/smartcontract/manifest/abi.go
+++ b/pkg/smartcontract/manifest/abi.go
@@ -4,7 +4,6 @@ import (
 	"cmp"
 	"errors"
 	"fmt"
-	"slices"
 
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
@@ -63,23 +62,14 @@ func (a *ABI) IsValid() error {
 			return fmt.Errorf("method %q/%d: %w", a.Methods[i].Name, len(a.Methods[i].Parameters), err)
 		}
 	}
-	if len(a.Methods) > 1 {
-		var methods = slices.Clone(a.Methods)
-		slices.SortFunc(methods, func(a, b Method) int {
-			return cmp.Or(
-				cmp.Compare(a.Name, b.Name),
-				cmp.Compare(len(a.Parameters), len(b.Parameters)),
-			)
-		})
-		for i := range methods {
-			if i == 0 {
-				continue
-			}
-			if methods[i].Name == methods[i-1].Name &&
-				len(methods[i].Parameters) == len(methods[i-1].Parameters) {
-				return errors.New("duplicate method specifications")
-			}
+	if sliceHasDups(a.Methods, func(a, b Method) int {
+		res := cmp.Compare(a.Name, b.Name)
+		if res != 0 {
+			return res
 		}
+		return cmp.Compare(len(a.Parameters), len(b.Parameters))
+	}) {
+		return errors.New("duplicate method specifications")
 	}
 	for i := range a.Events {
 		err := a.Events[i].IsValid()
@@ -87,14 +77,10 @@ func (a *ABI) IsValid() error {
 			return fmt.Errorf("event %q/%d: %w", a.Events[i].Name, len(a.Events[i].Parameters), err)
 		}
 	}
-	if len(a.Events) > 1 {
-		names := make([]string, len(a.Events))
-		for i := range a.Events {
-			names[i] = a.Events[i].Name
-		}
-		if stringsHaveDups(names) {
-			return errors.New("duplicate event names")
-		}
+	if sliceHasDups(a.Events, func(a, b Event) int {
+		return cmp.Compare(a.Name, b.Name)
+	}) {
+		return errors.New("duplicate event names")
 	}
 	return nil
 }
diff --git a/pkg/smartcontract/manifest/group.go b/pkg/smartcontract/manifest/group.go
index d2473cbca..9c7b7bd8b 100644
--- a/pkg/smartcontract/manifest/group.go
+++ b/pkg/smartcontract/manifest/group.go
@@ -6,7 +6,6 @@ import (
 	"encoding/json"
 	"errors"
 	"slices"
-	"sort"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
@@ -59,7 +58,7 @@ func (g Groups) AreValid(h util.Uint160) error {
 	for i := range g {
 		pkeys[i] = g[i].PublicKey
 	}
-	sort.Sort(pkeys)
+	slices.SortFunc(pkeys, (*keys.PublicKey).Cmp)
 	for i := range pkeys {
 		if i == 0 {
 			continue
diff --git a/pkg/smartcontract/manifest/manifest.go b/pkg/smartcontract/manifest/manifest.go
index 40cb168ce..f709c21ae 100644
--- a/pkg/smartcontract/manifest/manifest.go
+++ b/pkg/smartcontract/manifest/manifest.go
@@ -95,11 +95,8 @@ func (m *Manifest) IsValid(hash util.Uint160, checkSize bool) error {
 	if slices.Contains(m.SupportedStandards, "") {
 		return errors.New("invalid nameless supported standard")
 	}
-	if len(m.SupportedStandards) > 1 {
-		names := slices.Clone(m.SupportedStandards)
-		if stringsHaveDups(names) {
-			return errors.New("duplicate supported standards")
-		}
+	if sliceHasDups(m.SupportedStandards, strings.Compare) {
+		return errors.New("duplicate supported standards")
 	}
 	err = m.ABI.IsValid()
 	if err != nil {
@@ -122,11 +119,8 @@ func (m *Manifest) IsValid(hash util.Uint160, checkSize bool) error {
 	if m.Trusts.Value == nil && !m.Trusts.Wildcard {
 		return errors.New("invalid (null?) trusts")
 	}
-	if len(m.Trusts.Value) > 1 {
-		hashes := slices.Clone(m.Trusts.Value)
-		if permissionDescsHaveDups(hashes) {
-			return errors.New("duplicate trusted contracts")
-		}
+	if sliceHasDups(m.Trusts.Value, PermissionDesc.Compare) {
+		return errors.New("duplicate trusted contracts")
 	}
 	err = Permissions(m.Permissions).AreValid()
 	if err != nil {
diff --git a/pkg/smartcontract/manifest/parameter.go b/pkg/smartcontract/manifest/parameter.go
index ee3381bba..7cccb2b22 100644
--- a/pkg/smartcontract/manifest/parameter.go
+++ b/pkg/smartcontract/manifest/parameter.go
@@ -1,6 +1,7 @@
 package manifest
 
 import (
+	"cmp"
 	"errors"
 	"fmt"
 	"slices"
@@ -79,42 +80,28 @@ func (p Parameters) AreValid() error {
 			return fmt.Errorf("parameter #%d/%q: %w", i, p[i].Name, err)
 		}
 	}
-	if len(p) < 2 {
-		return nil
-	}
-	names := make([]string, len(p))
-	for i := range p {
-		names[i] = p[i].Name
-	}
-	if stringsHaveDups(names) {
+	if sliceHasDups(p, func(a, b Parameter) int {
+		return cmp.Compare(a.Name, b.Name)
+	}) {
 		return errors.New("duplicate parameter name")
 	}
 	return nil
 }
 
-// stringsHaveDups checks the given set of strings for duplicates. It modifies the slice given!
-func stringsHaveDups(strings []string) bool {
-	slices.Sort(strings)
-	for i := range strings {
+// sliceHasDups checks the slice for duplicate elements.
+func sliceHasDups[S ~[]E, E any](x S, cmp func(a, b E) int) bool {
+	if len(x) < 2 {
+		return false
+	}
+	if len(x) > 2 {
+		x = slices.Clone(x)
+		slices.SortFunc(x, cmp)
+	}
+	for i := range x {
 		if i == 0 {
 			continue
 		}
-		if strings[i] == strings[i-1] {
-			return true
-		}
-	}
-	return false
-}
-
-// permissionDescsHaveDups checks the given set of strings for duplicates. It modifies the slice given!
-func permissionDescsHaveDups(descs []PermissionDesc) bool {
-	slices.SortFunc(descs, PermissionDesc.Compare)
-	for i := range descs {
-		if i == 0 {
-			continue
-		}
-		j := i - 1
-		if descs[i].Compare(descs[j]) == 0 {
+		if cmp(x[i-1], x[i]) == 0 {
 			return true
 		}
 	}
diff --git a/pkg/smartcontract/manifest/permission.go b/pkg/smartcontract/manifest/permission.go
index a560669e8..254391981 100644
--- a/pkg/smartcontract/manifest/permission.go
+++ b/pkg/smartcontract/manifest/permission.go
@@ -119,11 +119,7 @@ func (p *Permission) IsValid() error {
 	if slices.Contains(p.Methods.Value, "") {
 		return errors.New("empty method name")
 	}
-	if len(p.Methods.Value) < 2 {
-		return nil
-	}
-	names := slices.Clone(p.Methods.Value)
-	if stringsHaveDups(names) {
+	if sliceHasDups(p.Methods.Value, cmp.Compare) {
 		return errors.New("duplicate method names")
 	}
 	return nil
@@ -137,14 +133,9 @@ func (ps Permissions) AreValid() error {
 			return err
 		}
 	}
-	if len(ps) < 2 {
-		return nil
-	}
-	contracts := make([]PermissionDesc, 0, len(ps))
-	for i := range ps {
-		contracts = append(contracts, ps[i].Contract)
-	}
-	if permissionDescsHaveDups(contracts) {
+	if sliceHasDups(ps, func(a, b Permission) int {
+		return a.Contract.Compare(b.Contract)
+	}) {
 		return errors.New("contracts have duplicates")
 	}
 	return nil