diff --git a/error.go b/error.go
index 44aecef25..c9b736855 100644
--- a/error.go
+++ b/error.go
@@ -23,7 +23,6 @@ import (
 	"net"
 	"os"
 	"reflect"
-	"syscall"
 	"time"
 
 	"go.elastic.co/apm/v2/model"
@@ -596,13 +595,6 @@ func init() {
 		details.SetAttr("syscall", syscallErr.Syscall)
 		details.Cause = append(details.Cause, syscallErr.Err)
 	}))
-	RegisterTypeErrorDetailer(reflect.TypeOf(syscall.Errno(0)), ErrorDetailerFunc(func(err error, details *ErrorDetails) {
-		errno := err.(syscall.Errno)
-		details.Code.String = errnoName(errno)
-		if details.Code.String == "" {
-			details.Code.Number = float64(errno)
-		}
-	}))
 }
 
 func errTemporary(err error) bool {
diff --git a/error_go120_test.go b/error_syscall.go
similarity index 55%
rename from error_go120_test.go
rename to error_syscall.go
index 623bbe373..0d286bcb6 100644
--- a/error_go120_test.go
+++ b/error_syscall.go
@@ -15,30 +15,21 @@
 // specific language governing permissions and limitations
 // under the License.
 
-//go:build go1.20
-// +build go1.20
+//go:build unix || windows
 
-package apm_test
+package apm // import "go.elastic.co/apm/v2"
 
 import (
-	"context"
-	"errors"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-
-	"go.elastic.co/apm/v2"
-	"go.elastic.co/apm/v2/apmtest"
+	"reflect"
+	"syscall"
 )
 
-func TestErrorCauseUnwrapJoined(t *testing.T) {
-	err := errors.Join(errors.New("cause1"), errors.New("cause2"))
-	_, _, errors := apmtest.WithTransaction(func(ctx context.Context) {
-		apm.CaptureError(ctx, err).Send()
-	})
-	require.Len(t, errors, 1)
-	require.Len(t, errors[0].Exception.Cause, 2)
-	assert.Equal(t, "cause1", errors[0].Exception.Cause[0].Message)
-	assert.Equal(t, "cause2", errors[0].Exception.Cause[1].Message)
+func init() {
+	RegisterTypeErrorDetailer(reflect.TypeOf(syscall.Errno(0)), ErrorDetailerFunc(func(err error, details *ErrorDetails) {
+		errno := err.(syscall.Errno)
+		details.Code.String = errnoName(errno)
+		if details.Code.String == "" {
+			details.Code.Number = float64(errno)
+		}
+	}))
 }
diff --git a/error_test.go b/error_test.go
index 8ca9c32b0..6d105f995 100644
--- a/error_test.go
+++ b/error_test.go
@@ -19,6 +19,7 @@ package apm_test
 
 import (
 	"context"
+	goerrors "errors"
 	"fmt"
 	"net"
 	"os"
@@ -52,6 +53,17 @@ func TestErrorID(t *testing.T) {
 	assert.Equal(t, model.TraceID(errorID), errors[0].ID)
 }
 
+func TestErrorCauseUnwrapJoined(t *testing.T) {
+	err := goerrors.Join(errors.New("cause1"), errors.New("cause2"))
+	_, _, errors := apmtest.WithTransaction(func(ctx context.Context) {
+		apm.CaptureError(ctx, err).Send()
+	})
+	require.Len(t, errors, 1)
+	require.Len(t, errors[0].Exception.Cause, 2)
+	assert.Equal(t, "cause1", errors[0].Exception.Cause[0].Message)
+	assert.Equal(t, "cause2", errors[0].Exception.Cause[1].Message)
+}
+
 func TestErrorsStackTrace(t *testing.T) {
 	modelError := sendError(t, &errorsStackTracer{
 		"zing", newErrorsStackTrace(0, 2),
diff --git a/error_unix.go b/error_unix.go
index 2666acd97..c2a8a4aec 100644
--- a/error_unix.go
+++ b/error_unix.go
@@ -15,8 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
-//go:build !windows
-// +build !windows
+//go:build unix
 
 package apm // import "go.elastic.co/apm/v2"
 
diff --git a/error_windows.go b/error_windows.go
index e0e1fdcf9..7655179e1 100644
--- a/error_windows.go
+++ b/error_windows.go
@@ -15,6 +15,8 @@
 // specific language governing permissions and limitations
 // under the License.
 
+//go:build windows
+
 package apm // import "go.elastic.co/apm/v2"
 
 import (