diff --git a/spec/raft/node_spec.cr b/spec/raft/node_spec.cr
index 66566f8..065f4af 100644
--- a/spec/raft/node_spec.cr
+++ b/spec/raft/node_spec.cr
@@ -518,7 +518,7 @@ describe Raft::Node do
   describe "peers" do
     it "exposes peer list including self" do
       node = create_test_node(1_u64, [2_u64, 3_u64])
-      node.peers.map(&.id).sort.should eq [1_u64, 2_u64, 3_u64]
+      node.peers.map(&.id).sort!.should eq [1_u64, 2_u64, 3_u64]
       node.peers.all?(&.voter?).should eq true
       node.close
     end
@@ -747,7 +747,7 @@ describe Raft::Node do
       node.close
     end
 
-    it "add_server rejects duplicate node" do
+    it "add_server rejects self-address-update and does not append a log entry" do
       config = Raft::Config.new
       config.election_timeout_min_ticks = 5_u32
       config.election_timeout_max_ticks = 5_u32
@@ -759,7 +759,102 @@ describe Raft::Node do
         3_u64 => create_test_node(3_u64, [1_u64, 2_u64], config),
       }
       elect_leader(nodes)
-      nodes[1_u64].add_server(2_u64).should eq false
+      leader_id = nodes.find! { |_, n| n.role == Raft::Role::Leader }.first
+      leader = nodes[leader_id]
+      own_peer_before = leader.peers.find! { |p| p.id == leader_id }
+      last_index_before = leader.log.last_index
+
+      # Attempting to update the leader's own address must be rejected
+      leader.add_server(leader_id, "127.0.0.1:9999").should eq false
+
+      # No log entry appended
+      leader.log.last_index.should eq last_index_before
+      # Own peer entry unchanged
+      own_peer_after = leader.peers.find! { |p| p.id == leader_id }
+      own_peer_after.address.should eq own_peer_before.address
+      nodes.each_value(&.close)
+    end
+
+    it "add_server rejects duplicate node with same address (no-op, returns true)" do
+      config = Raft::Config.new
+      config.election_timeout_min_ticks = 5_u32
+      config.election_timeout_max_ticks = 5_u32
+      config.heartbeat_ticks = 100_u32
+
+      nodes = {
+        1_u64 => create_test_node(1_u64, [2_u64, 3_u64], config),
+        2_u64 => create_test_node(2_u64, [1_u64, 3_u64], config),
+        3_u64 => create_test_node(3_u64, [1_u64, 2_u64], config),
+      }
+      elect_leader(nodes)
+      # Re-adding an existing peer with same (empty) address is a no-op: returns true, no new log entry
+      last_index_before = nodes[1_u64].log.last_index
+      nodes[1_u64].add_server(2_u64).should eq true
+      nodes[1_u64].log.last_index.should eq last_index_before
+      nodes.each_value(&.close)
+    end
+
+    it "add_server updates address for returning member with new address" do
+      config = Raft::Config.new
+      config.election_timeout_min_ticks = 5_u32
+      config.election_timeout_max_ticks = 5_u32
+      config.heartbeat_ticks = 100_u32
+
+      nodes = {
+        1_u64 => create_test_node(1_u64, [2_u64, 3_u64], config),
+        2_u64 => create_test_node(2_u64, [1_u64, 3_u64], config),
+        3_u64 => create_test_node(3_u64, [1_u64, 2_u64], config),
+      }
+      elect_leader(nodes)
+      # Peer 2 currently has no address; re-add with a new address
+      last_index_before = nodes[1_u64].log.last_index
+      nodes[1_u64].add_server(2_u64, "127.0.0.1:5679").should eq true
+      # A new configuration entry must have been appended
+      nodes[1_u64].log.last_index.should be > last_index_before
+      # Peer 2's address should be updated in the leader's peer list
+      peer2 = nodes[1_u64].peers.find { |p| p.id == 2_u64 }
+      peer2.should_not be_nil
+      peer2.not_nil!.address.should eq "127.0.0.1:5679"
+      nodes.each_value(&.close)
+    end
+
+    it "add_server updates address for returning learner with new address, preserving Learner role" do
+      config = Raft::Config.new
+      config.election_timeout_min_ticks = 5_u32
+      config.election_timeout_max_ticks = 5_u32
+      config.heartbeat_ticks = 100_u32
+
+      nodes = {
+        1_u64 => create_test_node(1_u64, [2_u64, 3_u64], config),
+        2_u64 => create_test_node(2_u64, [1_u64, 3_u64], config),
+        3_u64 => create_test_node(3_u64, [1_u64, 2_u64], config),
+      }
+      elect_leader(nodes)
+      leader = nodes[1_u64]
+
+      # First add node 4 as a learner
+      leader.add_server(4_u64, "127.0.0.1:5680").should eq true
+      peer4 = leader.peers.find { |p| p.id == 4_u64 }
+      peer4.not_nil!.learner?.should eq true
+      peer4.not_nil!.address.should eq "127.0.0.1:5680"
+
+      # Commit the first config change (same pattern as promote_learner test)
+      leader.take_messages.each do |target_id, msg|
+        nodes[target_id].step(msg) if nodes.has_key?(target_id)
+      end
+      [2_u64, 3_u64].each do |id|
+        nodes[id].take_messages.each do |target_id, msg|
+          leader.step(msg) if target_id == 1_u64
+        end
+      end
+
+      # Now re-add node 4 with a different address; role must stay Learner
+      last_index_before = leader.log.last_index
+      leader.add_server(4_u64, "127.0.0.1:9999").should eq true
+      leader.log.last_index.should be > last_index_before
+      peer4_updated = leader.peers.find { |p| p.id == 4_u64 }
+      peer4_updated.not_nil!.learner?.should eq true
+      peer4_updated.not_nil!.address.should eq "127.0.0.1:9999"
       nodes.each_value(&.close)
     end
 
@@ -1044,7 +1139,7 @@ describe Raft::Node do
 
       # Leader should send AppendEntries to all peers including the learner
       messages = leader.take_messages
-      target_ids = messages.map { |tid, _| tid }.uniq.sort
+      target_ids = messages.map { |tid, _| tid }.uniq!.sort!
       target_ids.should eq [2_u64, 3_u64, 4_u64]
 
       # Propose a value — quorum is still 2 (out of 3 voters)
@@ -1126,7 +1221,7 @@ describe Raft::Node do
 
       node_recovered = Raft::Node(TestData).new(id: 1_u64, peers: [2_u64, 3_u64], config: c1_recover, state_machine: TestStateMachine.new)
       node_recovered.peers.size.should eq 4
-      node_recovered.peers.map(&.id).sort.should eq [1_u64, 2_u64, 3_u64, 4_u64]
+      node_recovered.peers.map(&.id).sort!.should eq [1_u64, 2_u64, 3_u64, 4_u64]
       node_recovered.peers.all?(&.voter?).should eq true
 
       node_recovered.close
@@ -1301,7 +1396,7 @@ describe Raft::Node do
 
       # Add node 4 as learner
       leader.add_server(4_u64)
-      leader.peers.find { |p| p.id == 4_u64 }.not_nil!.learner?.should eq true
+      leader.peers.find! { |p| p.id == 4_u64 }.learner?.should eq true
 
       # Send AppendEntries to all peers including node 4
       messages = leader.take_messages
@@ -1432,7 +1527,7 @@ describe Raft::Node do
       # Node 4 should have peers now (applied config from leader)
       node4.peers.size.should be > 0
       # And should be a learner
-      node4.peers.find { |p| p.id == 4_u64 }.not_nil!.learner?.should eq true
+      node4.peers.find! { |p| p.id == 4_u64 }.learner?.should eq true
 
       # Drain any pending responses from replication
       node4.take_messages
diff --git a/src/raft/node.cr b/src/raft/node.cr
index eb9775e..db87737 100644
--- a/src/raft/node.cr
+++ b/src/raft/node.cr
@@ -312,12 +312,25 @@ module Raft
       true
     end
 
-    # Add a new node to the cluster as a learner.
-    # Returns false if not leader or node already exists.
+    # Add a new node to the cluster as a learner, or re-admit a returning member.
+    # - New id: adds as Learner, returns true.
+    # - Known id, different non-empty address: updates the stored address and replicates
+    #   the new configuration, returns true.
+    # - Known id, same address (or empty address passed): no-op, returns true.
+    # Returns false if not leader, if a configuration change is already in flight, or if node_id == @id.
     def add_server(node_id : NodeID, address : String = "") : Bool
       return false unless @role == Role::Leader
       return false if @pending_config_index > @commit_index
-      return false if @peers.any? { |p| p.id == node_id }
+      return false if node_id == @id
+      if existing = @peers.find { |p| p.id == node_id }
+        # Returning member: update address only if a non-empty new address differs.
+        return true if address.empty? || existing.address == address
+        new_peers = @peers.map do |p|
+          p.id == node_id ? Peer.new(p.id, p.role, address) : p
+        end
+        append_configuration(new_peers)
+        return true
+      end
       new_peers = @peers.dup
       new_peers << Peer.new(node_id, Peer::Role::Learner, address)
       append_configuration(new_peers)
@@ -513,7 +526,7 @@ module Raft
 
     private def cancel_pending_reads
       return if @pending_reads.empty? && @pending_apply.empty?
-      (@pending_reads + @pending_apply).each { |pr| pr.callback.call(nil) }
+      (@pending_reads + @pending_apply).each(&.callback.call(nil))
       @pending_reads.clear
       @pending_apply.clear
     end
@@ -1177,7 +1190,7 @@ module Raft
           f.write_bytes(0_u8, IO::ByteFormat::LittleEndian)
         end
         f.write_bytes(@peers.size.to_u32, IO::ByteFormat::LittleEndian)
-        @peers.each { |p| p.to_io(f) }
+        @peers.each(&.to_io(f))
         f.fsync
       end
       File.rename(tmp_path, path)
@@ -1207,7 +1220,7 @@ module Raft
     private def serialize_peers(peers : Array(Peer) = @peers) : Bytes
       io = IO::Memory.new
       io.write_bytes(peers.size.to_u32, IO::ByteFormat::LittleEndian)
-      peers.each { |p| p.to_io(io) }
+      peers.each(&.to_io(io))
       io.to_slice.dup
     end