diff --git a/tasks/swarm_init.rb b/tasks/swarm_init.rb
index f557d7c2..78c49af0 100755
--- a/tasks/swarm_init.rb
+++ b/tasks/swarm_init.rb
@@ -7,15 +7,15 @@
 
 def swarm_init(advertise_addr, autolock, cert_expiry, dispatcher_heartbeat, external_ca, force_new_cluster, listen_addr, max_snapshots, snapshot_interval)
   cmd_string = 'docker swarm init'
-  cmd_string << " --advertise-addr=#{advertise_addr}" unless advertise_addr.nil?
-  cmd_string << ' --autolock' unless autolock.nil?
-  cmd_string << ' --cert-expiry' unless cert_expiry.nil?
-  cmd_string << " --dispatcher-heartbeat=#{dispatcher_heartbeat}" unless dispatcher_heartbeat.nil?
-  cmd_string << " --external-ca=#{external_ca}" unless external_ca.nil?
-  cmd_string << ' --force-new-cluster' unless force_new_cluster.nil?
-  cmd_string << " --listen-addr=#{listen_addr}" unless listen_addr.nil?
-  cmd_string << " --max-snapshots=#{max_snapshots}" unless max_snapshots.nil?
-  cmd_string << " --snapshot-interval=#{snapshot_interval}" unless snapshot_interval.nil?
+  cmd_string += " --advertise-addr=#{advertise_addr}" unless advertise_addr.nil?
+  cmd_string += ' --autolock' unless autolock.nil?
+  cmd_string += ' --cert-expiry' unless cert_expiry.nil?
+  cmd_string += " --dispatcher-heartbeat=#{dispatcher_heartbeat}" unless dispatcher_heartbeat.nil?
+  cmd_string += " --external-ca=#{external_ca}" unless external_ca.nil?
+  cmd_string += ' --force-new-cluster' unless force_new_cluster.nil?
+  cmd_string += " --listen-addr=#{listen_addr}" unless listen_addr.nil?
+  cmd_string += " --max-snapshots=#{max_snapshots}" unless max_snapshots.nil?
+  cmd_string += " --snapshot-interval=#{snapshot_interval}" unless snapshot_interval.nil?
 
   stdout, stderr, status = Open3.capture3(cmd_string)
   raise Puppet::Error, "stderr: '#{stderr}'" if status != 0
diff --git a/tasks/swarm_join.rb b/tasks/swarm_join.rb
index fcffa4c4..c98471d5 100755
--- a/tasks/swarm_join.rb
+++ b/tasks/swarm_join.rb
@@ -7,10 +7,10 @@
 
 def swarm_join(advertise_addr, listen_addr, token, manager_ip)
   cmd_string = 'docker swarm join'
-  cmd_string << " --advertise-addr=#{advertise_addr}" unless advertise_addr.nil?
-  cmd_string << " --listen-addr=#{listen_addr}" unless listen_addr.nil?
-  cmd_string << " --token=#{token}" unless token.nil?
-  cmd_string << " #{manager_ip}" unless manager_ip.nil?
+  cmd_string += " --advertise-addr=#{advertise_addr}" unless advertise_addr.nil?
+  cmd_string += " --listen-addr=#{listen_addr}" unless listen_addr.nil?
+  cmd_string += " --token=#{token}" unless token.nil?
+  cmd_string += " #{manager_ip}" unless manager_ip.nil?
 
   stdout, stderr, status = Open3.capture3(cmd_string)
   raise Puppet::Error, "stderr: '#{stderr}'" if status != 0
diff --git a/tasks/swarm_leave.rb b/tasks/swarm_leave.rb
index a5abefa5..d6bc6bbb 100755
--- a/tasks/swarm_leave.rb
+++ b/tasks/swarm_leave.rb
@@ -7,7 +7,7 @@
 
 def swarm_leave(force)
   cmd_string = 'docker swarm leave '
-  cmd_string << ' -f' if force == 'true'
+  cmd_string += ' -f' if force == 'true'
   stdout, stderr, status = Open3.capture3(cmd_string)
   raise Puppet::Error, "stderr: '#{stderr}'" if status != 0
   stdout.strip
diff --git a/tasks/swarm_update.rb b/tasks/swarm_update.rb
index 214c2e3d..627923d8 100755
--- a/tasks/swarm_update.rb
+++ b/tasks/swarm_update.rb
@@ -7,8 +7,8 @@
 
 def swarm_update(image, service)
   cmd_string = 'docker service update'
-  cmd_string << " --image #{image}" unless image.nil?
-  cmd_string << " #{service}" unless service.nil?
+  cmd_string += " --image #{image}" unless image.nil?
+  cmd_string += " #{service}" unless service.nil?
 
   stdout, stderr, status = Open3.capture3(cmd_string)
   raise Puppet::Error, "stderr: '#{stderr}'" if status != 0