diff --git a/README.md b/README.md
index 9516432..7de6961 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,9 @@ If you want to use tokens in XML based configuration files to be replaced during
   - replace tokens in your updated configuration file
 
 ## Release notes
+**New in 3.5.1**
+- Fix issue when variable `System.ServerType` is not defined ([#147](https://github.com/qetza/vsts-replacetokens-task/issues/147)).
+
 **New in 3.5.0**
 - Add anonymous usage telemetry.
 - Ignore spaces between token prefix/suffix and variable name ([#143](https://github.com/qetza/vsts-replacetokens-task/issues/143)).
diff --git a/make.js b/make.js
index b901b99..6d125f9 100644
--- a/make.js
+++ b/make.js
@@ -190,8 +190,11 @@ updateTelemetryScript = function(instrumentationKey, taskVersion) {
     var scriptPath = path.join(binariesPath, 'task', 'telemetry.js');
     var script = fs.readFileSync(scriptPath, { encoding: 'utf8' });
 
+    if (instrumentationKey)
     script = script.replace(/const\s+instrumentationKey\s*=\s*'[^']*'\s*;/, "const instrumentationKey = '" + instrumentationKey + "';")
-    script = script.replace(/const\s+version\s*=\s*'[^']*'\s*;/, "const version = '" + taskVersion + "';");
+
+    if (taskVersion)
+        script = script.replace(/const\s+version\s*=\s*'[^']*'\s*;/, "const version = '" + taskVersion + "';");
 
     fs.writeFileSync(scriptPath, script);
 }
\ No newline at end of file
diff --git a/task/index.ts b/task/index.ts
index 0b00351..9ca0a03 100644
--- a/task/index.ts
+++ b/task/index.ts
@@ -394,7 +394,7 @@ var normalize = function (p: string): string {
 
 async function run() {
     let startTime: Date = new Date();
-    let serverType = tl.getVariable('System.ServerType').toLowerCase();
+    let serverType = tl.getVariable('System.ServerType');
     let telemetryEnabled = tl.getBoolInput('enableTelemetry', true) && tl.getVariable('REPLACETOKENS_DISABLE_TELEMETRY') !== 'true';
 
     let proxyUrl: string = undefined;
@@ -406,7 +406,7 @@ async function run() {
         account: crypto.createHash('sha256').update(tl.getVariable('system.collectionid')).digest('hex'),
         pipeline: crypto.createHash('sha256').update(tl.getVariable('system.teamprojectid') + tl.getVariable('system.definitionid')).digest('hex'),
         pipelineType: tl.getVariable('release.releaseid') ? 'release' : 'build',
-        serverType: !serverType || serverType !== 'hosted' ? 'server' : 'services',
+        serverType: !serverType || serverType.toLowerCase() !== 'hosted' ? 'server' : 'services',
     } as TelemetryEvent;
 
     try {
diff --git a/task/task.json b/task/task.json
index b46ff98..6000644 100644
--- a/task/task.json
+++ b/task/task.json
@@ -13,7 +13,7 @@
     "version": {
         "Major": 3,
         "Minor": 5,
-        "Patch": 0
+        "Patch": 1
     },
     "instanceNameFormat": "Replace tokens in $(targetFiles)",
     "minimumAgentVersion": "2.105.0",
diff --git a/vss-extension.json b/vss-extension.json
index 8705810..779c2d7 100644
--- a/vss-extension.json
+++ b/vss-extension.json
@@ -2,7 +2,7 @@
     "manifestVersion": 1,
     "id": "replacetokens",
     "name": "Replace Tokens",
-    "version": "3.5.0",
+    "version": "3.5.1",
     "public": true,
     "publisher": "qetza",
     "targets": [