diff --git a/api/errors.go b/api/errors.go
index 4a7648a12..e216f207d 100644
--- a/api/errors.go
+++ b/api/errors.go
@@ -62,6 +62,7 @@ const (
 	ErrNoSuchVersion
 	ErrNotImplemented
 	ErrPreconditionFailed
+	ErrNotModified
 	ErrRequestTimeTooSkewed
 	ErrSignatureDoesNotMatch
 	ErrMethodNotAllowed
@@ -494,6 +495,11 @@ var errorCodes = errorCodeMap{
 		Description:    "At least one of the pre-conditions you specified did not hold",
 		HTTPStatusCode: http.StatusPreconditionFailed,
 	},
+	ErrNotModified: {
+		Code:           "NotModified",
+		Description:    "The resource was not changed.",
+		HTTPStatusCode: http.StatusNotModified,
+	},
 	ErrRequestTimeTooSkewed: {
 		Code:           "RequestTimeTooSkewed",
 		Description:    "The difference between the request time and the server's time is too large.",
diff --git a/api/handler/copy.go b/api/handler/copy.go
index cb4776390..c9fea7ead 100644
--- a/api/handler/copy.go
+++ b/api/handler/copy.go
@@ -73,9 +73,8 @@ func (h *handler) CopyObjectHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	status := checkPreconditions(inf, args.Conditional)
-	if status != http.StatusOK {
-		w.WriteHeader(status)
+	if err = checkPreconditions(inf, args.Conditional); err != nil {
+		api.WriteErrorResponse(r.Context(), w, api.GetAPIError(api.ErrPreconditionFailed), r.URL)
 		return
 	}
 
diff --git a/api/handler/get.go b/api/handler/get.go
index eaef90a99..41b4b9673 100644
--- a/api/handler/get.go
+++ b/api/handler/get.go
@@ -96,9 +96,8 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	status := checkPreconditions(inf, args.Conditional)
-	if status != http.StatusOK {
-		w.WriteHeader(status)
+	if err = checkPreconditions(inf, args.Conditional); err != nil {
+		api.WriteErrorResponse(r.Context(), w, err, r.URL)
 		return
 	}
 
@@ -122,23 +121,23 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-func checkPreconditions(inf *layer.ObjectInfo, args *conditionalArgs) int {
+func checkPreconditions(inf *layer.ObjectInfo, args *conditionalArgs) error {
 	if len(args.IfMatch) > 0 && args.IfMatch != inf.HashSum {
-		return http.StatusPreconditionFailed
+		return api.GetAPIError(api.ErrPreconditionFailed)
 	}
 	if len(args.IfNoneMatch) > 0 && args.IfNoneMatch == inf.HashSum {
-		return http.StatusNotModified
+		return api.GetAPIError(api.ErrNotModified)
 	}
 	if args.IfModifiedSince != nil && inf.Created.Before(*args.IfModifiedSince) {
-		return http.StatusNotModified
+		return api.GetAPIError(api.ErrNotModified)
 	}
 	if args.IfUnmodifiedSince != nil && inf.Created.After(*args.IfUnmodifiedSince) {
 		if len(args.IfMatch) == 0 {
-			return http.StatusPreconditionFailed
+			return api.GetAPIError(api.ErrPreconditionFailed)
 		}
 	}
 
-	return http.StatusOK
+	return nil
 }
 
 func parseGetObjectArgs(headers http.Header) (*getObjectArgs, error) {
diff --git a/api/handler/get_test.go b/api/handler/get_test.go
index 9ebc51d5c..94a5d31ca 100644
--- a/api/handler/get_test.go
+++ b/api/handler/get_test.go
@@ -5,6 +5,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/nspcc-dev/neofs-s3-gw/api"
 	"github.com/nspcc-dev/neofs-s3-gw/api/layer"
 	"github.com/stretchr/testify/require"
 )
@@ -58,79 +59,79 @@ func TestPreconditions(t *testing.T) {
 		name     string
 		info     *layer.ObjectInfo
 		args     *conditionalArgs
-		expected int
+		expected error
 	}{
 		{
 			name:     "no conditions",
 			info:     new(layer.ObjectInfo),
 			args:     new(conditionalArgs),
-			expected: http.StatusOK,
+			expected: nil,
 		},
 		{
 			name:     "IfMatch true",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfMatch: etag},
-			expected: http.StatusOK,
+			expected: nil,
 		},
 		{
 			name:     "IfMatch false",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfMatch: etag2},
-			expected: http.StatusPreconditionFailed},
+			expected: api.GetAPIError(api.ErrPreconditionFailed)},
 		{
 			name:     "IfNoneMatch true",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfNoneMatch: etag2},
-			expected: http.StatusOK},
+			expected: nil},
 		{
 			name:     "IfNoneMatch false",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfNoneMatch: etag},
-			expected: http.StatusNotModified},
+			expected: api.GetAPIError(api.ErrNotModified)},
 		{
 			name:     "IfModifiedSince true",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfModifiedSince: &yesterday},
-			expected: http.StatusOK},
+			expected: nil},
 		{
 			name:     "IfModifiedSince false",
 			info:     newInfo(etag, yesterday),
 			args:     &conditionalArgs{IfModifiedSince: &today},
-			expected: http.StatusNotModified},
+			expected: api.GetAPIError(api.ErrNotModified)},
 		{
 			name:     "IfUnmodifiedSince true",
 			info:     newInfo(etag, yesterday),
 			args:     &conditionalArgs{IfUnmodifiedSince: &today},
-			expected: http.StatusOK},
+			expected: nil},
 		{
 			name:     "IfUnmodifiedSince false",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfUnmodifiedSince: &yesterday},
-			expected: http.StatusPreconditionFailed},
+			expected: api.GetAPIError(api.ErrPreconditionFailed)},
 
 		{
 			name:     "IfMatch true, IfUnmodifiedSince false",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfMatch: etag, IfUnmodifiedSince: &yesterday},
-			expected: http.StatusOK,
+			expected: nil,
 		},
 		{
 			name:     "IfMatch false, IfUnmodifiedSince true",
 			info:     newInfo(etag, yesterday),
 			args:     &conditionalArgs{IfMatch: etag2, IfUnmodifiedSince: &today},
-			expected: http.StatusPreconditionFailed,
+			expected: api.GetAPIError(api.ErrPreconditionFailed),
 		},
 		{
 			name:     "IfNoneMatch false, IfModifiedSince true",
 			info:     newInfo(etag, today),
 			args:     &conditionalArgs{IfNoneMatch: etag, IfModifiedSince: &yesterday},
-			expected: http.StatusNotModified,
+			expected: api.GetAPIError(api.ErrNotModified),
 		},
 		{
 			name:     "IfNoneMatch true, IfModifiedSince false",
 			info:     newInfo(etag, yesterday),
 			args:     &conditionalArgs{IfNoneMatch: etag2, IfModifiedSince: &today},
-			expected: http.StatusNotModified,
+			expected: api.GetAPIError(api.ErrNotModified),
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {