diff --git a/spec/site/core/disconnect_spec.rb b/spec/site/core/disconnect_spec.rb
index fe79fb17..8cd529c3 100644
--- a/spec/site/core/disconnect_spec.rb
+++ b/spec/site/core/disconnect_spec.rb
@@ -1,4 +1,5 @@
 RSpec.describe 'Site::Core' do
+  include Validator::CommandHelpers
 
   # Check that the site closed the connection as required when faced with
   # various types of incorrect behaviour from our side.
@@ -45,8 +46,7 @@ def site_proxy.acknowledge original
         end
 
         log "Stop sending watchdogs, site should not disconnect"
-        def site.send_watchdog now=nil
-        end
+        stop_sending_watchdogs(site)
         wait_task.wait
       end
     end
diff --git a/spec/site/tlc/clock_spec.rb b/spec/site/tlc/clock_spec.rb
index 94253e6a..4446da4d 100644
--- a/spec/site/tlc/clock_spec.rb
+++ b/spec/site/tlc/clock_spec.rb
@@ -5,6 +5,10 @@
   # Tests related to the clock.
   # When you set the clock, the adjusted time should be used
   # everywhere you get back a timestamp.
+  # Note that watchdog messages can be used to synchronize the clock,
+  # which can interfere with our tests. So we disable sending watchdogs
+  # during tests.
+
   
   describe 'Clock' do
     CLOCK = Time.new 2020,9,29,17,29,51,'+00:00'
@@ -50,6 +54,7 @@
     it 'is used for S0096 status response', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           status_list = { S0096: [
             :year,
@@ -97,6 +102,7 @@
     it 'is used for S0096 response timestamp', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           status_list = { S0096: [
             :year,
@@ -134,6 +140,7 @@
     it 'is used for aggregated status timestamp', core: '>=3.1.5', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           result = site.request_aggregated_status Validator.config['main_component'], collect!: {
             timeout: Validator.config['timeouts']['status_response']
@@ -158,6 +165,7 @@
     it 'is used for M0001 response timestamp', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           result = set_functional_position 'NormalControl'
           collector = result[:collector]
@@ -180,6 +188,7 @@
     it 'is used for M0104 response timestamp', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           result = set_functional_position 'NormalControl'
           collector = result[:collector]
@@ -206,6 +215,7 @@
     it 'is used for alarm timestamp', :programming, sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do                           # set clock
           with_alarm_activated(task, site, 'A0302') do |alarm|   # raise alarm, by activating input
             alarm_time = Time.parse( alarm.attributes["aTs"] )
@@ -228,6 +238,7 @@
     it 'is used for watchdog timestamp', sxl: '>=1.0.7' do |example|
       Validator::Site.connected do |task,supervisor,site|
         prepare task, site
+        stop_sending_watchdogs(site)  # avoid time synchronization by watchdogs
         with_clock_set CLOCK do
           log "Checking watchdog timestamp"
           collector = RSMP::Collector.new site, task:task, type: "Watchdog", num: 1, timeout: Validator.config['timeouts']['watchdog']
diff --git a/spec/support/command_helpers.rb b/spec/support/command_helpers.rb
index ebaa3960..e2bc7296 100644
--- a/spec/support/command_helpers.rb
+++ b/spec/support/command_helpers.rb
@@ -455,6 +455,13 @@ def reset_clock
     send_command_and_confirm @task, command_list, "Reset clock to #{now}"
   end
 
+  def stop_sending_watchdogs(site)
+    # monkey-patch the site object by redefining
+    # the send_watchdog method to do nothing
+    def site.send_watchdog now=nil
+    end
+  end
+
   def with_clock_set clock, &block
     result = set_clock clock
     yield result