diff --git a/crates/ruma-common/CHANGELOG.md b/crates/ruma-common/CHANGELOG.md
index ef6df0eb..de8fcbb8 100644
--- a/crates/ruma-common/CHANGELOG.md
+++ b/crates/ruma-common/CHANGELOG.md
@@ -1,5 +1,10 @@
 # [unreleased]
 
+Bug fixes:
+
+* HTML-relevant characters (`<`, `>`, etc) in plaintext replies are now escaped
+  during creation of the rich reply
+
 Breaking changes:
 
 * Remove deprecated `EventType` enum
diff --git a/crates/ruma-common/src/events/room/message/reply.rs b/crates/ruma-common/src/events/room/message/reply.rs
index 2ae771db..e9d6c2ab 100644
--- a/crates/ruma-common/src/events/room/message/reply.rs
+++ b/crates/ruma-common/src/events/room/message/reply.rs
@@ -48,6 +48,29 @@ fn get_message_quote_fallbacks(original_message: &OriginalRoomMessageEvent) -> (
     }
 }
 
+/// Converts a plaintext body to HTML, escaping any characters that would cause problems.
+fn escape_html_entities(body: &str) -> String {
+    let mut escaped_body = String::with_capacity(body.len());
+    for c in body.chars() {
+        // Escape reserved HTML entities and new lines.
+        // <https://developer.mozilla.org/en-US/docs/Glossary/Entity#reserved_characters>
+        let s = match c {
+            '&' => Some("&amp;"),
+            '<' => Some("&lt;"),
+            '>' => Some("&gt;"),
+            '"' => Some("&quot;"),
+            '\n' => Some("<br>"),
+            _ => None,
+        };
+        if let Some(s) = s {
+            escaped_body.push_str(s);
+        } else {
+            escaped_body.push(c);
+        }
+    }
+    escaped_body
+}
+
 fn formatted_or_plain_body(
     formatted: Option<&FormattedBody>,
     body: &str,
@@ -64,25 +87,7 @@ fn formatted_or_plain_body(
         #[cfg(not(feature = "unstable-sanitize"))]
         formatted_body.body.clone()
     } else {
-        let mut escaped_body = String::with_capacity(body.len());
-        for c in body.chars() {
-            // Escape reserved HTML entities and new lines.
-            // <https://developer.mozilla.org/en-US/docs/Glossary/Entity#reserved_characters>
-            let s = match c {
-                '&' => Some("&amp;"),
-                '<' => Some("&lt;"),
-                '>' => Some("&gt;"),
-                '"' => Some("&quot;"),
-                '\n' => Some("<br>"),
-                _ => None,
-            };
-            if let Some(s) = s {
-                escaped_body.push_str(s);
-            } else {
-                escaped_body.push(c);
-            }
-        }
-        escaped_body
+        escape_html_entities(body)
     }
 }
 
@@ -97,7 +102,7 @@ fn formatted_or_plain_body(
 /// [HTML tags and attributes]: https://spec.matrix.org/v1.4/client-server-api/#mroommessage-msgtypes
 /// [rich reply fallbacks]: https://spec.matrix.org/v1.4/client-server-api/#fallbacks-for-rich-replies
 pub fn plain_and_formatted_reply_body(
-    body: impl fmt::Display,
+    body: &str,
     formatted: Option<impl fmt::Display>,
     original_message: &OriginalRoomMessageEvent,
 ) -> (String, String) {
@@ -106,7 +111,7 @@ pub fn plain_and_formatted_reply_body(
     let plain = format!("{quoted}\n{body}");
     let html = match formatted {
         Some(formatted) => format!("{quoted_html}{formatted}"),
-        None => format!("{quoted_html}{body}"),
+        None => format!("{quoted_html}{}", escape_html_entities(body)),
     };
 
     (plain, html)
diff --git a/crates/ruma-common/tests/events/room_message.rs b/crates/ruma-common/tests/events/room_message.rs
index 48c8f1a2..4d26001a 100644
--- a/crates/ruma-common/tests/events/room_message.rs
+++ b/crates/ruma-common/tests/events/room_message.rs
@@ -8,8 +8,9 @@ use ruma_common::{
         key::verification::VerificationMethod,
         room::{
             message::{
-                AudioMessageEventContent, KeyVerificationRequestEventContent, MessageType,
-                OriginalRoomMessageEvent, RoomMessageEventContent, TextMessageEventContent,
+                AudioMessageEventContent, ForwardThread, KeyVerificationRequestEventContent,
+                MessageType, OriginalRoomMessageEvent, RoomMessageEventContent,
+                TextMessageEventContent,
             },
             MediaSource,
         },
@@ -434,6 +435,53 @@ fn content_deserialization_failure() {
     assert_matches!(from_json_value::<RoomMessageEventContent>(json_data), Err(_));
 }
 
+#[test]
+fn escape_tags_in_plain_reply_body() {
+    let first_message = OriginalRoomMessageEvent {
+        content: RoomMessageEventContent::text_plain("Usage: cp <source> <destination>"),
+        event_id: event_id!("$143273582443PhrSn:example.org").to_owned(),
+        origin_server_ts: MilliSecondsSinceUnixEpoch(uint!(10_000)),
+        room_id: room_id!("!testroomid:example.org").to_owned(),
+        sender: user_id!("@user:example.org").to_owned(),
+        unsigned: MessageLikeUnsigned::default(),
+    };
+    let second_message = RoomMessageEventContent::text_plain("Usage: rm <path>")
+        .make_reply_to(&first_message, ForwardThread::Yes);
+
+    let body = assert_matches!(
+        first_message.content.msgtype,
+        MessageType::Text(TextMessageEventContent { body, formatted: None, .. }) => body
+    );
+    assert_eq!(body, "Usage: cp <source> <destination>");
+
+    let (body, formatted) = assert_matches!(
+        second_message.msgtype,
+        MessageType::Text(TextMessageEventContent { body, formatted, .. }) => (body, formatted)
+    );
+    assert_eq!(
+        body,
+        "\
+        > <@user:example.org> Usage: cp <source> <destination>\n\
+        Usage: rm <path>\
+        "
+    );
+    let formatted = formatted.unwrap();
+    assert_eq!(
+        formatted.body,
+        "\
+        <mx-reply>\
+            <blockquote>\
+                <a href=\"https://matrix.to/#/!testroomid:example.org/$143273582443PhrSn:example.org\">In reply to</a> \
+                <a href=\"https://matrix.to/#/@user:example.org\">@user:example.org</a>\
+                <br>\
+                Usage: cp &lt;source&gt; &lt;destination&gt;\
+            </blockquote>\
+        </mx-reply>\
+        Usage: rm &lt;path&gt;\
+        "
+    );
+}
+
 #[test]
 #[cfg(feature = "unstable-sanitize")]
 fn reply_sanitize() {