diff --git a/src/base.rs b/src/base.rs
index fef5b11..0b2b8d0 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -1146,6 +1146,22 @@ impl RoomInfo {
 
         return top;
     }
+
+    /// Checks if a given user has reacted with the given emoji on the given event
+    pub fn user_reactions_contains(
+        &mut self,
+        user_id: &UserId,
+        event_id: &EventId,
+        emoji: &str,
+    ) -> bool {
+        if let Some(reactions) = self.reactions.get(event_id) {
+            reactions
+                .values()
+                .any(|(annotation, user)| annotation == emoji && user == user_id)
+        } else {
+            false
+        }
+    }
 }
 
 /// Generate a [CompletionMap] for Emoji shortcodes.
diff --git a/src/windows/room/chat.rs b/src/windows/room/chat.rs
index 8f49672..8f42d72 100644
--- a/src/windows/room/chat.rs
+++ b/src/windows/room/chat.rs
@@ -372,6 +372,13 @@ impl ChatState {
                     },
                 };
 
+                if info.user_reactions_contains(&settings.profile.user_id, &event_id, &emoji) {
+                    let msg = format!("You’ve already reacted to this message with {}", emoji);
+                    let err = UIError::Failure(msg);
+
+                    return Err(err);
+                }
+
                 let reaction = Annotation::new(event_id, emoji);
                 let msg = ReactionEventContent::new(reaction);
                 let _ = room.send(msg).await.map_err(IambError::from)?;