diff --git a/web/app.rb b/web/app.rb
index 20b73fe..7ee75bb 100644
--- a/web/app.rb
+++ b/web/app.rb
@@ -1064,6 +1064,9 @@ def insert_message(db, m)
 
   ensure_unknown_node(db, from_id || raw_from_id, m["from_num"], heard_time: rx_time)
 
+  update_sender_last_heard =
+    encrypted && !encrypted.strip.empty? && from_id && rx_time
+
   row = [
     msg_id,
     rx_time,
@@ -1133,6 +1136,18 @@ def insert_message(db, m)
       end
     end
   end
+
+  if update_sender_last_heard
+    with_busy_retry do
+      db.execute <<~SQL, [rx_time, rx_time, from_id, rx_time]
+                   UPDATE nodes
+                      SET last_heard = ?,
+                          first_heard = COALESCE(first_heard, ?)
+                    WHERE node_id = ?
+                      AND COALESCE(last_heard, 0) <= ?
+                 SQL
+    end
+  end
 end
 
 # Resolve a node reference to the canonical node ID when possible.
diff --git a/web/spec/app_spec.rb b/web/spec/app_spec.rb
index 187427c..aa1955f 100644
--- a/web/spec/app_spec.rb
+++ b/web/spec/app_spec.rb
@@ -1004,6 +1004,13 @@ RSpec.describe "Potato Mesh Sinatra app" do
         expect(row["to_id"]).to eq(receiver_id)
         expect(row["text"]).to be_nil
         expect(row["encrypted"]).to eq(encrypted_b64)
+
+        node_row = db.get_first_row(
+          "SELECT last_heard FROM nodes WHERE node_id = ?",
+          [sender_id],
+        )
+
+        expect(node_row["last_heard"]).to eq(reference_time.to_i)
       end
 
       get "/api/messages"