diff --git a/src/m2d/converters/event-to-message.js b/src/m2d/converters/event-to-message.js
index cff08f0..c014a3e 100644
--- a/src/m2d/converters/event-to-message.js
+++ b/src/m2d/converters/event-to-message.js
@@ -1051,11 +1051,11 @@ async function eventToMessage(event, guild, channel, di) {
 		// Combine requested mentions with detected written mentions to get the full list
 		if (Array.isArray(event.content["m.mentions"].user_ids)) {
 			for (const mxid of event.content["m.mentions"].user_ids) {
-				const user_id = select("sim", "user_id", {mxid}).pluck().get()
-				if (!user_id) continue
-				allowedMentionsUsers.push(
-					select("sim_proxy", "proxy_owner_id", {user_id}).pluck().get() || user_id
-				)
+				let user_id = select("sim", "user_id", {mxid}).pluck().get()
+				if (!user_id) continue // only for discord users
+				user_id = select("sim_proxy", "proxy_owner_id", {user_id}).pluck().get() || user_id // convert to sim proxy owner's ID
+				if (!user_id.match(/^[0-9]+$/)) continue // mentioned sim does not have a real discord user ID (i.e. it's a webhook)
+				allowedMentionsUsers.push(user_id)
 			}
 		}
 		// Specific mentions were requested, so do not parse users
diff --git a/src/m2d/converters/event-to-message.test.js b/src/m2d/converters/event-to-message.test.js
index 5dd0af7..6b22773 100644
--- a/src/m2d/converters/event-to-message.test.js
+++ b/src/m2d/converters/event-to-message.test.js
@@ -1711,6 +1711,63 @@ test("event2message: rich reply to a sim user, explicitly disabling mentions in
 	)
 })
 
+test("event2message: rich reply to a webhook with m.mentions", async t => {
+	t.deepEqual(
+		await eventToMessage({
+			"type": "m.room.message",
+			"sender": "@cadence:cadence.moe",
+			"content": {
+				"msgtype": "m.text",
+				"body": "> <@_ooye_webhook_spidey_bot:cadence.moe:cadence.moe> Slow news day.\n\nTesting this reply, ignore",
+				"format": "org.matrix.custom.html",
+				"formatted_body": "<mx-reply><blockquote><a href=\"https://matrix.to/#/!fGgIymcYWOqjbSRUdV:cadence.moe/$Fxy8SMoJuTduwReVkHZ1uHif9EuvNx36Hg79cltiA04?via=cadence.moe&via=feather.onl\">In reply to</a> <a href=\"https://matrix.to/#/@_ooye_webhook_spidey_bot:cadence.moe:cadence.moe\">@_ooye_webhook_spidey_bot:cadence.moe:cadence.moe</a><br>Slow news day.</blockquote></mx-reply>Testing this reply, ignore",
+				"m.relates_to": {
+					"m.in_reply_to": {
+						"event_id": "$Fxy8SMoJuTduwReVkHZ1uHif9EuvNx36Hg79cltiA04"
+					}
+				},
+				"m.mentions": {
+					user_ids: ["@_ooye_webhook_spidey_bot:cadence.moe"]
+				}
+			},
+			"origin_server_ts": 1693029683016,
+			"unsigned": {
+				"age": 91,
+				"transaction_id": "m1693029682894.510"
+			},
+			"event_id": "$v_Gtr-bzv9IVlSLBO5DstzwmiDd-GSFaNfHX66IupV8",
+			"room_id": "!fGgIymcYWOqjbSRUdV:cadence.moe"
+		}, data.guild.general, data.channel.general, {
+			api: {
+				getEvent: mockGetEvent(t, "!fGgIymcYWOqjbSRUdV:cadence.moe", "$Fxy8SMoJuTduwReVkHZ1uHif9EuvNx36Hg79cltiA04", {
+					type: "m.room.message",
+					content: {
+						msgtype: "m.text",
+						body: "Slow news day."
+					},
+					sender: "@_ooye_webhook_spidey_bot:cadence.moe"
+				})
+			}
+		}),
+		{
+			ensureJoined: [],
+			messagesToDelete: [],
+			messagesToEdit: [],
+			messagesToSend: [{
+				username: "cadence [they]",
+				content: "-# > <:L1:1144820033948762203><:L2:1144820084079087647>https://discord.com/channels/112760669178241024/687028734322147344/1144865310588014633 **@Spidey Bot**:"
+					+ " Slow news day."
+					+ "\nTesting this reply, ignore",
+				avatar_url: "https://bridge.example.org/download/matrix/cadence.moe/azCAhThKTojXSZJRoWwZmhvU?preset=avatar",
+				allowed_mentions: {
+					parse: ["roles"],
+					users: []
+				}
+			}]
+		}
+	)
+})
+
 test("event2message: rich reply to a rich reply to a multi-line message should correctly strip reply fallback", async t => {
 	t.deepEqual(
 		await eventToMessage({
diff --git a/test/ooye-test-data.sql b/test/ooye-test-data.sql
index 1662320..524e1fe 100644
--- a/test/ooye-test-data.sql
+++ b/test/ooye-test-data.sql
@@ -41,8 +41,8 @@ INSERT INTO sim (user_id, username, sim_name, mxid) VALUES
 ('772659086046658620', 'cadence.worm', 'cadence', '@_ooye_cadence:cadence.moe'),
 ('196188877885538304', 'ampflower', 'ampflower', '@_ooye_ampflower:cadence.moe'),
 ('1458668878107381800', 'Evil Lillith (she/her)', 'evil_lillith_sheher', '@_ooye_evil_lillith_sheher:cadence.moe'),
-('197126718400626689', 'infinidoge1337', 'infinidoge1337', '@_ooye_infinidoge1337:cadence.moe');
-
+('197126718400626689', 'infinidoge1337', 'infinidoge1337', '@_ooye_infinidoge1337:cadence.moe'),
+('webhook_spidey_bot', 'Spidey Bot', 'webhook_spidey_bot', '@_ooye_webhook_spidey_bot:cadence.moe');
 
 INSERT INTO sim_member (mxid, room_id, hashed_profile_content) VALUES
 ('@_ooye_bojack_horseman:cadence.moe', '!hYnGGlPHlbujVVfktC:cadence.moe', NULL),