diff --git a/apidiff.sh b/apidiff.sh
index 6024096..d30b7cb 100755
--- a/apidiff.sh
+++ b/apidiff.sh
@@ -8,20 +8,30 @@ if ! test -d tmp/mox-$prevversion; then
 fi
 (rm -r tmp/apidiff || exit 0)
 mkdir -p tmp/apidiff/$prevversion tmp/apidiff/next
-(rm apidiff/next.txt || exit 0)
-(
-echo "Below are the incompatible changes between $prevversion and next, per package."
-echo
-) >>apidiff/next.txt
+(rm apidiff/next.txt apidiff/next.txt.new 2>/dev/null || exit 0)
 for p in $(cat apidiff/packages.txt); do
 	if ! test -d tmp/mox-$prevversion/$p; then
 		continue
 	fi
 	(cd tmp/mox-$prevversion && apidiff -w ../apidiff/$prevversion/$p.api ./$p)
 	apidiff -w tmp/apidiff/next/$p.api ./$p
-	(
-	echo '#' $p
-	apidiff -incompatible tmp/apidiff/$prevversion/$p.api tmp/apidiff/next/$p.api
-	echo
-	) >>apidiff/next.txt
+	apidiff -incompatible tmp/apidiff/$prevversion/$p.api tmp/apidiff/next/$p.api >$p.diff
+	if test -s $p.diff; then
+		(
+		echo '#' $p
+		cat $p.diff
+		echo
+		) >>apidiff/next.txt.new
+	fi
+	rm $p.diff
 done
+if test -s apidiff/next.txt.new; then
+	(
+	echo "Below are the incompatible changes between $prevversion and next, per package."
+	echo
+	cat apidiff/next.txt.new
+	) >apidiff/next.txt
+	rm apidiff/next.txt.new
+else
+	mv apidiff/next.txt.new apidiff/next.txt
+fi
diff --git a/apidiff/next.txt b/apidiff/next.txt
index e69de29..6120436 100644
--- a/apidiff/next.txt
+++ b/apidiff/next.txt
@@ -0,0 +1,5 @@
+Below are the incompatible changes between v0.0.13 and next, per package.
+
+# webhook
+- PartStructure: removed
+
diff --git a/queue/hook.go b/queue/hook.go
index 700bec4..94fb88d 100644
--- a/queue/hook.go
+++ b/queue/hook.go
@@ -3,6 +3,7 @@ package queue
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -796,7 +797,7 @@ func Incoming(ctx context.Context, log mlog.Log, acc *store.Account, messageID s
 
 		log.Debug("composing webhook for incoming message")
 
-		structure, err := webhook.PartStructure(log, &part)
+		structure, err := PartStructure(log, &part)
 		if err != nil {
 			return fmt.Errorf("parsing part structure: %v", err)
 		}
@@ -912,6 +913,38 @@ func Incoming(ctx context.Context, log mlog.Log, acc *store.Account, messageID s
 	return nil
 }
 
+// PartStructure returns a webhook.Structure for a parsed message part.
+func PartStructure(log mlog.Log, p *message.Part) (webhook.Structure, error) {
+	parts := make([]webhook.Structure, len(p.Parts))
+	for i := range p.Parts {
+		var err error
+		parts[i], err = PartStructure(log, &p.Parts[i])
+		if err != nil && !errors.Is(err, message.ErrParamEncoding) {
+			return webhook.Structure{}, err
+		}
+	}
+	disp, filename, err := p.DispositionFilename()
+	if err != nil && errors.Is(err, message.ErrParamEncoding) {
+		log.Debugx("parsing disposition/filename", err)
+	} else if err != nil {
+		return webhook.Structure{}, err
+	}
+	s := webhook.Structure{
+		ContentType:        strings.ToLower(p.MediaType + "/" + p.MediaSubType),
+		ContentTypeParams:  p.ContentTypeParams,
+		ContentID:          p.ContentID,
+		ContentDisposition: strings.ToLower(disp),
+		Filename:           filename,
+		DecodedSize:        p.DecodedSize,
+		Parts:              parts,
+	}
+	// Replace nil map with empty map, for easier to use JSON.
+	if s.ContentTypeParams == nil {
+		s.ContentTypeParams = map[string]string{}
+	}
+	return s, nil
+}
+
 func isAutomated(h textproto.MIMEHeader) bool {
 	l := []string{"List-Id", "List-Unsubscribe", "List-Unsubscribe-Post", "Precedence"}
 	for _, k := range l {
diff --git a/queue/hook_test.go b/queue/hook_test.go
index 75cebd1..b1190c5 100644
--- a/queue/hook_test.go
+++ b/queue/hook_test.go
@@ -82,7 +82,7 @@ func TestHookIncoming(t *testing.T) {
 		tcheck(t, err, "decode incoming webhook")
 		in.Meta.Received = in.Meta.Received.Local() // For TZ UTC.
 
-		structure, err := webhook.PartStructure(pkglog, &part)
+		structure, err := PartStructure(pkglog, &part)
 		tcheck(t, err, "part structure")
 
 		expIncoming := webhook.Incoming{
diff --git a/webapisrv/server.go b/webapisrv/server.go
index 8505ba9..8e53198 100644
--- a/webapisrv/server.go
+++ b/webapisrv/server.go
@@ -44,7 +44,6 @@ import (
 	"github.com/mjl-/mox/store"
 	"github.com/mjl-/mox/webapi"
 	"github.com/mjl-/mox/webauth"
-	"github.com/mjl-/mox/webhook"
 	"github.com/mjl-/mox/webops"
 )
 
@@ -1263,7 +1262,7 @@ func (s server) MessageGet(ctx context.Context, req webapi.MessageGetRequest) (r
 		MailboxName:         mb.Name,
 	}
 
-	structure, err := webhook.PartStructure(log, &p)
+	structure, err := queue.PartStructure(log, &p)
 	xcheckf(err, "parsing structure")
 
 	result := webapi.MessageGetResult{
diff --git a/webapisrv/server_test.go b/webapisrv/server_test.go
index 995accb..3e507c5 100644
--- a/webapisrv/server_test.go
+++ b/webapisrv/server_test.go
@@ -25,7 +25,6 @@ import (
 	"github.com/mjl-/mox/queue"
 	"github.com/mjl-/mox/store"
 	"github.com/mjl-/mox/webapi"
-	"github.com/mjl-/mox/webhook"
 )
 
 var ctxbg = context.Background()
@@ -418,7 +417,7 @@ func TestServer(t *testing.T) {
 	tcheckf(t, err, "reading raw message")
 	part, err := message.EnsurePart(log.Logger, true, bytes.NewReader(b.Bytes()), int64(b.Len()))
 	tcheckf(t, err, "parsing raw message")
-	structure, err := webhook.PartStructure(log, &part)
+	structure, err := queue.PartStructure(log, &part)
 	tcheckf(t, err, "part structure")
 	tcompare(t, structure, msgRes.Structure)
 
diff --git a/webhook/webhook.go b/webhook/webhook.go
index 9582c55..bda6249 100644
--- a/webhook/webhook.go
+++ b/webhook/webhook.go
@@ -8,12 +8,7 @@
 package webhook
 
 import (
-	"errors"
-	"strings"
 	"time"
-
-	"github.com/mjl-/mox/message"
-	"github.com/mjl-/mox/mlog"
 )
 
 // OutgoingEvent is an activity for an outgoing delivery. Either generated by the
@@ -145,35 +140,3 @@ type Structure struct {
 	DecodedSize        int64             // Size of content after decoding content-transfer-encoding. For text and HTML parts, this can be larger than the data returned since this size includes \r\n line endings.
 	Parts              []Structure       // Subparts of a multipart message, possibly recursive.
 }
-
-// PartStructure returns a Structure for a parsed message part.
-func PartStructure(log mlog.Log, p *message.Part) (Structure, error) {
-	parts := make([]Structure, len(p.Parts))
-	for i := range p.Parts {
-		var err error
-		parts[i], err = PartStructure(log, &p.Parts[i])
-		if err != nil && !errors.Is(err, message.ErrParamEncoding) {
-			return Structure{}, err
-		}
-	}
-	disp, filename, err := p.DispositionFilename()
-	if err != nil && errors.Is(err, message.ErrParamEncoding) {
-		log.Debugx("parsing disposition/filename", err)
-	} else if err != nil {
-		return Structure{}, err
-	}
-	s := Structure{
-		ContentType:        strings.ToLower(p.MediaType + "/" + p.MediaSubType),
-		ContentTypeParams:  p.ContentTypeParams,
-		ContentID:          p.ContentID,
-		ContentDisposition: strings.ToLower(disp),
-		Filename:           filename,
-		DecodedSize:        p.DecodedSize,
-		Parts:              parts,
-	}
-	// Replace nil map with empty map, for easier to use JSON.
-	if s.ContentTypeParams == nil {
-		s.ContentTypeParams = map[string]string{}
-	}
-	return s, nil
-}