diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 2ee0f67382..603dff9e77 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -375,9 +375,14 @@ namespace ts {
         }
     }
 
+    /**
+     * Parses non quoted strings separated by comma e.g. "a,b" would result in string array ["a", "b"]
+     * @param s
+     * @param existingValue
+     */
     function parseMultiValueStringArray(s: string, existingValue: string[]) {
         let value: string[] = existingValue || [];
-        let hasError: boolean;
+        let hasError = false;
         let currentString = "";
         if (s) {
             for (let i = 0; i < s.length; i++) {
@@ -480,8 +485,7 @@ namespace ts {
         }
         // Check if the value asked was string[] and value provided was not string[]
         else if (expectedType !== "string[]" ||
-            typeof jsonValue !== "object" ||
-            typeof jsonValue.length !== "number" ||
+            !(jsonValue instanceof Array) ||
             forEach(<string[]>jsonValue, individualValue => typeof individualValue !== "string")) {
             // Not expectedType
             errors.push(createCompilerDiagnostic(Diagnostics.Compiler_option_0_requires_a_value_of_type_1, opt.name, expectedType));
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index f6daf4880b..999b8bd6df 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -14,10 +14,10 @@ namespace ts {
     
     export const version = "1.7.0";
 
-    export function findConfigFile(searchPath: string, moduleResolutionHost: ModuleResolutionHost): string {
+    export function findConfigFile(searchPath: string, fileExists: (fileName: string) => boolean): string {
         let fileName = "tsconfig.json";
         while (true) {
-            if (moduleResolutionHost.fileExists(fileName)) {
+            if (fileExists(fileName)) {
                 return fileName;
             }
             let parentPath = getDirectoryPath(searchPath);
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index 8c1bf962aa..a0c3cc642e 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -188,7 +188,7 @@ namespace ts {
         }
         else if (commandLine.fileNames.length === 0 && isJSONSupported()) {
             let searchPath = normalizePath(sys.getCurrentDirectory());
-            configFileName = findConfigFile(searchPath, sys);
+            configFileName = findConfigFile(searchPath, sys.fileExists);
         }
 
         if (commandLine.fileNames.length === 0 && !configFileName) {
diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
index a250cb3daa..700423a721 100644
--- a/src/harness/projectsRunner.ts
+++ b/src/harness/projectsRunner.ts
@@ -195,7 +195,7 @@ class ProjectRunner extends RunnerBase {
                 assert(!inputFiles || inputFiles.length === 0, "cannot specify input files and project option together");
             }
             else if (!inputFiles || inputFiles.length === 0) {
-                configFileName = ts.findConfigFile("", { fileExists, readFile: getSourceFileText });
+                configFileName = ts.findConfigFile("", fileExists);
             }
 
             if (configFileName) {