diff --git a/scripts/build/findUpDir.js b/scripts/build/findUpDir.js
new file mode 100644
index 00000000000..fab301c6dcd
--- /dev/null
+++ b/scripts/build/findUpDir.js
@@ -0,0 +1,21 @@
+const { join, resolve, dirname } = require("path");
+const { existsSync } = require("fs");
+
+// search directories upward to avoid hard-wired paths based on the
+// build tree (same as src/harness/findUpDir.ts)
+
+function findUpFile(name) {
+    let dir = __dirname;
+    while (true) {
+        const fullPath = join(dir, name);
+        if (existsSync(fullPath)) return fullPath;
+        const up = resolve(dir, "..");
+        if (up === dir) return name; // it'll fail anyway
+        dir = up;
+    }
+}
+exports.findUpFile = findUpFile;
+
+const findUpRoot = () =>
+    findUpRoot.cached || (findUpRoot.cached = dirname(findUpFile("Gulpfile.js")));
+exports.findUpRoot = findUpRoot;
diff --git a/scripts/build/projects.js b/scripts/build/projects.js
index 954f37af84e..38db816e23b 100644
--- a/scripts/build/projects.js
+++ b/scripts/build/projects.js
@@ -1,5 +1,7 @@
 // @ts-check
 const { exec, Debouncer } = require("./utils");
+const { resolve } = require("path");
+const { findUpRoot } = require("./findUpDir");
 
 class ProjectQueue {
     /**
@@ -33,7 +35,13 @@ class ProjectQueue {
     }
 }
 
-const projectBuilder = new ProjectQueue((projects, lkg, force) => exec(process.execPath, [lkg ? "./lib/tsc" : "./built/local/tsc", "-b", ...(force ? ["--force"] : []), ...projects], { hidePrompt: true }));
+const execTsc = (lkg, ...args) =>
+    exec(process.execPath,
+         [resolve(findUpRoot(), lkg ? "./lib/tsc" : "./built/local/tsc"),
+          "-b", ...args],
+         { hidePrompt: true })
+
+const projectBuilder = new ProjectQueue((projects, lkg, force) => execTsc(lkg, ...(force ? ["--force"] : []), ...projects));
 
 /**
  * @param {string} project
@@ -43,14 +51,14 @@ const projectBuilder = new ProjectQueue((projects, lkg, force) => exec(process.e
  */
 exports.buildProject = (project, { lkg, force } = {}) => projectBuilder.enqueue(project, { lkg, force });
 
-const projectCleaner = new ProjectQueue((projects, lkg) => exec(process.execPath, [lkg ? "./lib/tsc" : "./built/local/tsc", "-b", "--clean", ...projects], { hidePrompt: true }));
+const projectCleaner = new ProjectQueue((projects, lkg) => execTsc(lkg, "--clean", ...projects));
 
 /**
  * @param {string} project
  */
 exports.cleanProject = (project) => projectCleaner.enqueue(project);
 
-const projectWatcher = new ProjectQueue((projects) => exec(process.execPath, ["./lib/tsc", "-b", "--watch", ...projects], { hidePrompt: true }));
+const projectWatcher = new ProjectQueue((projects) => execTsc(true, "--watch", ...projects));
 
 /**
  * @param {string} project
diff --git a/scripts/build/tests.js b/scripts/build/tests.js
index 7fee32566dd..10c6db79cf1 100644
--- a/scripts/build/tests.js
+++ b/scripts/build/tests.js
@@ -9,6 +9,7 @@ const log = require("fancy-log");
 const cmdLineOptions = require("./options");
 const { CancellationToken } = require("prex");
 const { exec } = require("./utils");
+const { findUpFile } = require("./findUpDir");
 
 const mochaJs = require.resolve("mocha/bin/_mocha");
 exports.localBaseline = "tests/baselines/local/";
@@ -73,11 +74,11 @@ async function runConsoleTests(runJs, defaultReporter, runInParallel, watchMode,
     /** @type {string[]} */
     let args = [];
 
-    // timeout normally isn"t necessary but Travis-CI has been timing out on compiler baselines occasionally
+    // timeout normally isn't necessary but Travis-CI has been timing out on compiler baselines occasionally
     // default timeout is 2sec which really should be enough, but maybe we just need a small amount longer
     if (!runInParallel) {
         args.push(mochaJs);
-        args.push("-R", "scripts/failed-tests");
+        args.push("-R", findUpFile("scripts/failed-tests.js"));
         args.push("-O", '"reporter=' + reporter + (keepFailed ? ",keepFailed=true" : "") + '"');
         if (tests) {
             args.push("-g", `"${tests}"`);
diff --git a/src/harness/findUpDir.ts b/src/harness/findUpDir.ts
new file mode 100644
index 00000000000..03b5ebdf285
--- /dev/null
+++ b/src/harness/findUpDir.ts
@@ -0,0 +1,21 @@
+namespace findUpDir {
+    import { join, resolve, dirname } from "path";
+    import { existsSync } from "fs";
+
+    // search directories upward to avoid hard-wired paths based on the
+    // build tree (same as scripts/build/findUpDir.js)
+
+    export function findUpFile(name: string) {
+        let dir = __dirname;
+        while (true) {
+            const fullPath = join(dir, name);
+            if (existsSync(fullPath)) return fullPath;
+            const up = resolve(dir, "..");
+            if (up === dir) return name; // it'll fail anyway
+            dir = up;
+        }
+    }
+
+    export const findUpRoot: { (): string; cached?: string; } = () =>
+        findUpRoot.cached ||= dirname(findUpFile("Gulpfile.js"));
+}