diff --git a/calibrate.go b/calibrate.go
index 0ed9091..9babeca 100644
--- a/calibrate.go
+++ b/calibrate.go
@@ -2,6 +2,7 @@ package i18n
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"time"
 
@@ -48,7 +49,7 @@ func CalibrateDomains(ctx context.Context, modelA, modelB inference.TextModel,
 	samples []CalibrationSample, opts ...ClassifyOption) (*CalibrationStats, error) {
 
 	if len(samples) == 0 {
-		return nil, fmt.Errorf("calibrate: empty sample set")
+		return nil, errors.New("calibrate: empty sample set")
 	}
 
 	cfg := defaultClassifyConfig()
diff --git a/reversal/reference.go b/reversal/reference.go
index e5e4d03..2b8e95c 100644
--- a/reversal/reference.go
+++ b/reversal/reference.go
@@ -1,7 +1,7 @@
 package reversal
 
 import (
-	"fmt"
+	"errors"
 	"math"
 	"sort"
 )
@@ -45,7 +45,7 @@ type ImprintClassification struct {
 // per unique domain label.
 func BuildReferences(tokeniser *Tokeniser, samples []ClassifiedText) (*ReferenceSet, error) {
 	if len(samples) == 0 {
-		return nil, fmt.Errorf("empty sample set")
+		return nil, errors.New("empty sample set")
 	}
 
 	// Group imprints by domain.
@@ -60,7 +60,7 @@ func BuildReferences(tokeniser *Tokeniser, samples []ClassifiedText) (*Reference
 	}
 
 	if len(grouped) == 0 {
-		return nil, fmt.Errorf("no samples with domain labels")
+		return nil, errors.New("no samples with domain labels")
 	}
 
 	rs := &ReferenceSet{Domains: make(map[string]*ReferenceDistribution)}
diff --git a/service.go b/service.go
index 17df471..67adde9 100644
--- a/service.go
+++ b/service.go
@@ -3,6 +3,7 @@ package i18n
 import (
 	"embed"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/fs"
 	"maps"
@@ -97,7 +98,7 @@ func NewWithLoader(loader Loader, opts ...Option) (*Service, error) {
 
 	langs := loader.Languages()
 	if len(langs) == 0 {
-		return nil, fmt.Errorf("no languages available from loader")
+		return nil, errors.New("no languages available from loader")
 	}
 
 	for _, lang := range langs {
@@ -181,7 +182,7 @@ func (s *Service) SetLanguage(lang string) error {
 		return fmt.Errorf("invalid language tag %q: %w", lang, err)
 	}
 	if len(s.availableLangs) == 0 {
-		return fmt.Errorf("no languages available")
+		return errors.New("no languages available")
 	}
 	matcher := language.NewMatcher(s.availableLangs)
 	bestMatch, _, confidence := matcher.Match(requestedLang)