diff --git a/go.mod b/go.mod
index 54d2081..6ee9e3d 100644
--- a/go.mod
+++ b/go.mod
@@ -15,7 +15,7 @@ require (
 	github.com/zyedidia/clipboard v1.0.4
 	go.mau.fi/libsignal v0.1.0
 	go.mau.fi/util v0.3.1-0.20240208085450-32294da153ab
-	go.mau.fi/whatsmeow v0.0.0-20240208121856-0ef58f1cef30
+	go.mau.fi/whatsmeow v0.0.0-20240209124521-50c00bd025be
 	golang.org/x/crypto v0.19.0
 	golang.org/x/exp v0.0.0-20240205201215-2c58cdc269a3
 	golang.org/x/image v0.15.0
diff --git a/go.sum b/go.sum
index 1fe6df4..5dfdffc 100644
--- a/go.sum
+++ b/go.sum
@@ -55,8 +55,8 @@ go.mau.fi/libsignal v0.1.0 h1:vAKI/nJ5tMhdzke4cTK1fb0idJzz1JuEIpmjprueC+c=
 go.mau.fi/libsignal v0.1.0/go.mod h1:R8ovrTezxtUNzCQE5PH30StOQWWeBskBsWE55vMfY9I=
 go.mau.fi/util v0.3.1-0.20240208085450-32294da153ab h1:XZ8W5vHWlXSGmHn1U+Fvbh+xZr9wuHTvbY+qV7aybDY=
 go.mau.fi/util v0.3.1-0.20240208085450-32294da153ab/go.mod h1:rRypwgXVEPILomtFPyQcnbOeuRqf+nRN84vh/CICq4w=
-go.mau.fi/whatsmeow v0.0.0-20240208121856-0ef58f1cef30 h1:gwmgU+l0OSww0Me3N022hLdZk7lnEoK8XeaWGlESG1I=
-go.mau.fi/whatsmeow v0.0.0-20240208121856-0ef58f1cef30/go.mod h1:lQHbhaG/fI+6hfGqz5Vzn2OBJBEZ05H0kCP6iJXriN4=
+go.mau.fi/whatsmeow v0.0.0-20240209124521-50c00bd025be h1:VQKRp4od2zRwu99T9bKeIj+ck+mgevVyJBGU+O2DZUU=
+go.mau.fi/whatsmeow v0.0.0-20240209124521-50c00bd025be/go.mod h1:lQHbhaG/fI+6hfGqz5Vzn2OBJBEZ05H0kCP6iJXriN4=
 go.mau.fi/zeroconfig v0.1.2 h1:DKOydWnhPMn65GbXZOafgkPm11BvFashZWLct0dGFto=
 go.mau.fi/zeroconfig v0.1.2/go.mod h1:NcSJkf180JT+1IId76PcMuLTNa1CzsFFZ0nBygIQM70=
 golang.org/x/crypto v0.19.0 h1:ENy+Az/9Y1vSrlrvBSyna3PITt4tiZLf7sgCjZBX7Wo=
diff --git a/msgconv/to-whatsapp.go b/msgconv/to-whatsapp.go
index 54cb5fa..1dbc3d1 100644
--- a/msgconv/to-whatsapp.go
+++ b/msgconv/to-whatsapp.go
@@ -17,8 +17,10 @@
 package msgconv
 
 import (
+	"bytes"
 	"context"
 	"fmt"
+	"image"
 	"strconv"
 	"strings"
 	"time"
@@ -130,6 +132,18 @@ func parseGeoURI(uri string) (lat, long float64, err error) {
 	return
 }
 
+func clampTo400(w, h int) (int, int) {
+	if w > 400 {
+		h = h * 400 / w
+		w = 400
+	}
+	if h > 400 {
+		w = w * 400 / h
+		h = 400
+	}
+	return w, h
+}
+
 func (mc *MessageConverter) reuploadMediaToWhatsApp(ctx context.Context, evt *event.Event, content *event.MessageEventContent) (*waMediaTransport.WAMediaTransport, string, error) {
 	data, mimeType, fileName, err := mc.downloadMatrixMedia(ctx, content)
 	if err != nil {
@@ -161,26 +175,41 @@ func (mc *MessageConverter) reuploadMediaToWhatsApp(ctx context.Context, evt *ev
 		}
 		customInfo["fi.mau.gif"] = true
 	}
+	if content.MsgType == event.MsgImage && content.Info.Width == 0 {
+		cfg, _, _ := image.DecodeConfig(bytes.NewReader(data))
+		content.Info.Width, content.Info.Height = cfg.Width, cfg.Height
+	}
 	mediaType := msgToMediaType(content.MsgType)
 	uploaded, err := mc.GetE2EEClient(ctx).Upload(ctx, data, mediaType)
 	if err != nil {
 		return nil, "", err
 	}
+	w, h := clampTo400(content.Info.Width, content.Info.Height)
+	if w == 0 && content.MsgType == event.MsgImage {
+		w, h = 400, 400
+	}
 	mediaTransport := &waMediaTransport.WAMediaTransport{
 		Integral: &waMediaTransport.WAMediaTransport_Integral{
 			FileSHA256:        uploaded.FileSHA256,
 			MediaKey:          uploaded.MediaKey,
 			FileEncSHA256:     uploaded.FileEncSHA256,
 			DirectPath:        uploaded.DirectPath,
-			MediaKeyTimestamp: time.Now().UnixMilli(),
+			MediaKeyTimestamp: time.Now().Unix(),
 		},
 		Ancillary: &waMediaTransport.WAMediaTransport_Ancillary{
 			FileLength: uint64(len(data)),
 			Mimetype:   mimeType,
-			Thumbnail:  nil,
-			ObjectID:   uploaded.ObjectID,
+			// This field is extremely required for some reason.
+			// Messenger iOS & Android will refuse to display the media if it's not present.
+			// iOS also requires that width and height are non-empty.
+			Thumbnail: &waMediaTransport.WAMediaTransport_Ancillary_Thumbnail{
+				ThumbnailWidth:  uint32(w),
+				ThumbnailHeight: uint32(h),
+			},
+			ObjectID: uploaded.ObjectID,
 		},
 	}
+	fmt.Printf("Uploaded media transport: %+v\n", mediaTransport)
 	return mediaTransport, fileName, nil
 }