diff --git a/lib/support/guest_customization.rb b/lib/support/guest_customization.rb
index 3a1db90..c8cc46e 100644
--- a/lib/support/guest_customization.rb
+++ b/lib/support/guest_customization.rb
@@ -195,7 +195,7 @@ def guest_customization_identity_windows
 
       RbVmomi::VIM::CustomizationSysprep.new(
         guiUnattended: RbVmomi::VIM::CustomizationGuiUnattended.new(
-          timeZone: timezone.to_i || DEFAULT_WINDOWS_TIMEZONE,
+          timeZone: windows_timezone_convert(timezone || DEFAULT_WINDOWS_TIMEZONE),
           autoLogon: false,
           autoLogonCount: 1,
           password: customization_pass
@@ -242,11 +242,36 @@ def valid_linux_timezone?(input)
     def valid_windows_timezone?(input)
       # Accept decimals and hex
       # See https://support.microsoft.com/en-us/help/973627/microsoft-time-zone-index-values
-      windows_timezone_pattern = /^([0-9]+|0x[0-9a-fA-F]+)$/
+      windows_timezone_pattern = /^((-){,1}[0-9]+|0x[0-9a-fA-F]+)$/
 
       input.to_s.match? windows_timezone_pattern
     end
 
+    # convert the value provided to a signed int
+    #
+    # @param input - Value to convert
+    # @returns [Integer] of converted value
+    def windows_timezone_convert(input)
+      mid = 2**(32 - 1)
+      max = 2**32
+      if input.is_a?(String)
+        if input.match?(/^0x[0-9a-fA-F]+$/)
+          input = input.to_i(16)
+        else
+          input = input.to_i
+        end
+      end
+      if input.is_a?(Integer)
+        input = input
+      else
+        input = input.to_i(16)
+      end
+      if input >= mid
+        input -= max
+      end
+      input
+    end
+
     # Check for format of Windows Product IDs
     #
     # @param [String] input String to check
diff --git a/spec/unit/support/clone_vm_spec.rb b/spec/unit/support/clone_vm_spec.rb
index d8a0776..a2222a0 100644
--- a/spec/unit/support/clone_vm_spec.rb
+++ b/spec/unit/support/clone_vm_spec.rb
@@ -271,5 +271,43 @@
         expect(subject.networks_to_add.first[:name]).to eq "my-network-2"
       end
     end
+
+    windows_timezone_tests = [
+      ["Coordinated Universal Time", [0x80000050, "0x80000050", "-2147483568", -2147483568], -2147483568],
+      ["Eastern Time (US & Canada)", ["35", 35, 0x23, "0x23"], 35],
+      ["Central Time (US & Canada)", ["20", 20, 0x14, "0x14"], 20],
+      ["Dublin, Edinburgh, Lisbon, London", ["85", 85, "0x55", 0x55], 85],
+      ["Istanbul", [-2147483560, "-2147483560", 0x80000058, "0x80000058"], -2147483560],
+      ["Casablanca", [-2147483571, "-2147483571", 0x8000004d, "0x8000004d"], -2147483571],
+    ]
+    windows_timezone_tests.each do |this_timezone|
+      context "when windows guest_customization timezone for \"#{this_timezone[0]}\" is provided" do
+        this_timezone[1].each do |val|
+          before do
+            allow(event_manager).to receive(:QueryEvents).and_return([RbVmomi::VIM::CustomizationSucceeded()])
+            options[:vm_os] = "windows"
+            options[:guest_customization] = {
+              timeout_task: 1,
+              timezone: val,
+              product_id: "D2N9P-3P6X9-2R39C-7RTCD-MDVJX",
+              org_name: "chef",
+              dns_domain: "chef.io",
+              dns_server_list: [],
+              dns_suffix_list: [],
+            }
+          end
+          it "helper method properly validates the passed timezone" do
+            expect(subject.valid_windows_timezone?(options[:guest_customization][:timezone])).to be_truthy
+          end
+          it "helper method properly converts the passed timezone to a 32-bit signed integer" do
+            expect(subject.windows_timezone_convert(options[:guest_customization][:timezone])).to eq this_timezone[2]
+          end
+          it "sets guest customization data with the correct timezone code" do
+            expect(source_vm).to receive(:CloneVM_Task).with(spec: a_hash_including(customization: a_hash_including(identity: a_hash_including(guiUnattended: a_hash_including(timeZone: this_timezone[2])))), folder: folder_id, name: vm_name).and_return(clone_vm_task)
+            subject.clone
+          end
+        end
+      end
+    end
   end
 end