diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index c2202f14b55..64e2509f9f6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4719,8 +4719,7 @@ namespace ts {
                 }
                 // Handle export default expressions
                 if (isSourceFile(declaration)) {
-                    Debug.assert(isJsonSourceFile(declaration));
-                    const jsonSourceFile = <JsonSourceFile>declaration;
+                    const jsonSourceFile = cast(declaration, isJsonSourceFile);
                     return links.type = jsonSourceFile.statements.length ? checkExpression(jsonSourceFile.statements[0].expression) : emptyObjectType;
                 }
                 if (declaration.kind === SyntaxKind.ExportAssignment) {
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 395291750ce..0f75d445c00 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1076,6 +1076,8 @@ namespace ts {
 
     /**
      * Convert the json syntax tree into the json value and report errors
+     * This returns the json value (apart from checking errors) only if returnValue provided is true.
+     * Otherwise it just checks the errors and returns undefined
      */
     /*@internal*/
     export function convertToObjectWorker(
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index ed436718209..4f052581c20 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2433,7 +2433,7 @@ namespace ts {
         switch (extension) {
             case Extension.Ts:
             case Extension.Dts:
-            case Extension.Json:
+            case Extension.Json: // Since module is resolved to json file only when --resolveJsonModule, we dont need further check
                 // These are always allowed.
                 return undefined;
             case Extension.Tsx:
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index f326840afa1..3f7affcc044 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1076,26 +1076,20 @@ namespace ts {
         });
     }
 
-    export function getTsConfigObjectLiteralExpression(tsConfigSourceFile: TsConfigSourceFile) {
+    export function getTsConfigObjectLiteralExpression(tsConfigSourceFile: TsConfigSourceFile | undefined) {
         if (tsConfigSourceFile && tsConfigSourceFile.statements.length) {
             const expression = tsConfigSourceFile.statements[0].expression;
             return isObjectLiteralExpression(expression) && expression;
         }
     }
 
-    export function getTsConfigPropArrayElementValue(tsConfigSourceFile: TsConfigSourceFile, propKey: string, elementValue: string): StringLiteral {
+    export function getTsConfigPropArrayElementValue(tsConfigSourceFile: TsConfigSourceFile | undefined, propKey: string, elementValue: string): StringLiteral | undefined {
         const jsonObjectLiteral = getTsConfigObjectLiteralExpression(tsConfigSourceFile);
-        if (jsonObjectLiteral) {
-            for (const property of getPropertyAssignment(jsonObjectLiteral, propKey)) {
-                if (isArrayLiteralExpression(property.initializer)) {
-                    for (const element of property.initializer.elements) {
-                        if (isStringLiteral(element) && element.text === elementValue) {
-                            return element;
-                        }
-                    }
-                }
-            }
-        }
+        return jsonObjectLiteral &&
+            firstDefined(getPropertyAssignment(jsonObjectLiteral, propKey), property =>
+                isArrayLiteralExpression(property.initializer) ?
+                    find(property.initializer.elements, (element): element is StringLiteral => isStringLiteral(element) && element.text === elementValue) :
+                    undefined);
     }
 
     export function getContainingFunction(node: Node): SignatureDeclaration {