diff --git a/scripts/processDiagnosticMessages.ts b/scripts/processDiagnosticMessages.ts
index 20085022c04..dd66564b134 100644
--- a/scripts/processDiagnosticMessages.ts
+++ b/scripts/processDiagnosticMessages.ts
@@ -1,4 +1,5 @@
 /// <reference path="../src/compiler/sys.ts" />
+/// <reference path="../src/compiler/core.ts" />
 
 interface DiagnosticDetails {
     category: string;
@@ -9,57 +10,55 @@ interface DiagnosticDetails {
 type InputDiagnosticMessageTable = ts.Map<DiagnosticDetails>;
 
 function main(): void {
-    var sys = ts.sys;
+    const sys = ts.sys;
     if (sys.args.length < 1) {
-        sys.write("Usage:" + sys.newLine)
+        sys.write("Usage:" + sys.newLine);
         sys.write("\tnode processDiagnosticMessages.js <diagnostic-json-input-file>" + sys.newLine);
         return;
     }
 
     function writeFile(fileName: string, contents: string) {
-        // TODO: Fix path joining
-        var inputDirectory = inputFilePath.substr(0,inputFilePath.lastIndexOf("/"));
-        var fileOutputPath = inputDirectory + "/" + fileName;
+        const inputDirectory = ts.getDirectoryPath(inputFilePath);
+        const fileOutputPath = ts.combinePaths(inputDirectory, fileName);
         sys.writeFile(fileOutputPath, contents);
     }
 
-    var inputFilePath = sys.args[0].replace(/\\/g, "/");
-    var inputStr = sys.readFile(inputFilePath);
+    const inputFilePath = sys.args[0].replace(/\\/g, "/");
+    const inputStr = sys.readFile(inputFilePath);
 
-    var diagnosticMessagesJson: { [key: string]: DiagnosticDetails } = JSON.parse(inputStr);
-    // Check that there are no duplicates.
-    const seenNames = ts.createMap<true>();
-    for (const name of Object.keys(diagnosticMessagesJson)) {
-        if (seenNames.has(name))
-            throw new Error(`Name ${name} appears twice`);
-        seenNames.set(name, true);
-    }
+    const diagnosticMessagesJson: { [key: string]: DiagnosticDetails } = JSON.parse(inputStr);
 
     const diagnosticMessages: InputDiagnosticMessageTable = ts.createMapFromTemplate(diagnosticMessagesJson);
 
-    var infoFileOutput = buildInfoFileOutput(diagnosticMessages);
+    const outputFilesDir = ts.getDirectoryPath(inputFilePath);
+    const thisFilePathRel = ts.getRelativePathToDirectoryOrUrl(outputFilesDir, sys.getExecutingFilePath(),
+        sys.getCurrentDirectory(), ts.createGetCanonicalFileName(sys.useCaseSensitiveFileNames), /* isAbsolutePathAnUrl */ false);
+
+    const infoFileOutput = buildInfoFileOutput(diagnosticMessages, "./diagnosticInformationMap.generated.ts", thisFilePathRel);
     checkForUniqueCodes(diagnosticMessages);
     writeFile("diagnosticInformationMap.generated.ts", infoFileOutput);
 
-    var messageOutput = buildDiagnosticMessageOutput(diagnosticMessages);
+    const messageOutput = buildDiagnosticMessageOutput(diagnosticMessages);
     writeFile("diagnosticMessages.generated.json", messageOutput);
 }
 
 function checkForUniqueCodes(diagnosticTable: InputDiagnosticMessageTable) {
     const allCodes: { [key: number]: true | undefined } = [];
     diagnosticTable.forEach(({ code }) => {
-        if (allCodes[code])
+        if (allCodes[code]) {
             throw new Error(`Diagnostic code ${code} appears more than once.`);
+        }
         allCodes[code] = true;
     });
 }
 
-function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable): string {
-    var result =
-        '// <auto-generated />\r\n' +
-        '/// <reference path="types.ts" />\r\n' +
-        '/* @internal */\r\n' +
-        'namespace ts {\r\n' +
+function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable, inputFilePathRel: string, thisFilePathRel: string): string {
+    let result =
+        "// <auto-generated />\r\n" +
+        "// generated from '" + inputFilePathRel + "' by '" + thisFilePathRel + "'\r\n" +
+        "/// <reference path=\"types.ts\" />\r\n" +
+        "/* @internal */\r\n" +
+        "namespace ts {\r\n" +
         "    function diag(code: number, category: DiagnosticCategory, key: string, message: string): DiagnosticMessage {\r\n" +
         "        return { code, category, key, message };\r\n" +
         "    }\r\n" +
@@ -70,20 +69,20 @@ function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable): string
         result += `        ${propName}: diag(${code}, DiagnosticCategory.${category}, "${createKey(propName, code)}", ${JSON.stringify(name)}),\r\n`;
     });
 
-    result += '    };\r\n}';
+    result += "    };\r\n}";
 
     return result;
 }
 
 function buildDiagnosticMessageOutput(messageTable: InputDiagnosticMessageTable): string {
-    let result = '{';
+    let result = "{";
     messageTable.forEach(({ code }, name) => {
         const propName = convertPropertyName(name);
         result += `\r\n  "${createKey(propName, code)}" : "${name.replace(/[\"]/g, '\\"')}",`;
     });
 
     // Shave trailing comma, then add newline and ending brace
-    result = result.slice(0, result.length - 1) + '\r\n}';
+    result = result.slice(0, result.length - 1) + "\r\n}";
 
     // Assert that we generated valid JSON
     JSON.parse(result);
@@ -91,15 +90,15 @@ function buildDiagnosticMessageOutput(messageTable: InputDiagnosticMessageTable)
     return result;
 }
 
-function createKey(name: string, code: number) : string {
-    return name.slice(0, 100) + '_' + code;
+function createKey(name: string, code: number): string {
+    return name.slice(0, 100) + "_" + code;
 }
 
 function convertPropertyName(origName: string): string {
-    var result = origName.split("").map(char => {
-        if (char === '*') { return "_Asterisk"; }
-        if (char === '/') { return "_Slash"; }
-        if (char === ':') { return "_Colon"; }
+    let result = origName.split("").map(char => {
+        if (char === "*") { return "_Asterisk"; }
+        if (char === "/") { return "_Slash"; }
+        if (char === ":") { return "_Colon"; }
         return /\w/.test(char) ? char : "_";
     }).join("");
 
@@ -107,7 +106,7 @@ function convertPropertyName(origName: string): string {
     result = result.replace(/_+/g, "_");
 
     // remove any leading underscore, unless it is followed by a number.
-    result = result.replace(/^_([^\d])/, "$1")
+    result = result.replace(/^_([^\d])/, "$1");
 
     // get rid of all trailing underscores.
     result = result.replace(/_$/, "");