diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0834322ff48..e2c6e4d6a53 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -95,6 +95,7 @@ namespace ts {
             getTypeAtLocation: getTypeOfNode,
             getPropertySymbolOfDestructuringAssignment,
             signatureToString,
+            indexSignatureToString,
             typeToString,
             getSymbolDisplayBuilder,
             symbolToString,
@@ -2035,6 +2036,15 @@ namespace ts {
             return result;
         }
 
+        function indexSignatureToString(info: IndexInfo, kind: SyntaxKind, enclosingDeclaration?: Node): string {
+            const writer = getSingleLineStringWriter();
+            getSymbolDisplayBuilder().buildIndexSignatureDisplay(info, writer, kind, enclosingDeclaration);
+            const result = writer.string();
+            releaseStringWriter(writer);
+
+            return result;
+        }
+
         function typeToString(type: Type, enclosingDeclaration?: Node, flags?: TypeFormatFlags): string {
             const writer = getSingleLineStringWriter();
             getSymbolDisplayBuilder().buildTypeDisplay(type, writer, enclosingDeclaration, flags);
@@ -2459,26 +2469,6 @@ namespace ts {
                     buildSymbolDisplay(type.symbol, writer, enclosingDeclaration, SymbolFlags.Value, SymbolFormatFlags.None, typeFormatFlags);
                 }
 
-                function writeIndexSignature(info: IndexInfo, keyword: SyntaxKind) {
-                    if (info) {
-                        if (info.isReadonly) {
-                            writeKeyword(writer, SyntaxKind.ReadonlyKeyword);
-                            writeSpace(writer);
-                        }
-                        writePunctuation(writer, SyntaxKind.OpenBracketToken);
-                        writer.writeParameter(info.declaration ? declarationNameToString(info.declaration.parameters[0].name) : "x");
-                        writePunctuation(writer, SyntaxKind.ColonToken);
-                        writeSpace(writer);
-                        writeKeyword(writer, keyword);
-                        writePunctuation(writer, SyntaxKind.CloseBracketToken);
-                        writePunctuation(writer, SyntaxKind.ColonToken);
-                        writeSpace(writer);
-                        writeType(info.type, TypeFormatFlags.None);
-                        writePunctuation(writer, SyntaxKind.SemicolonToken);
-                        writer.writeLine();
-                    }
-                }
-
                 function writePropertyWithModifiers(prop: Symbol) {
                     if (isReadonlySymbol(prop)) {
                         writeKeyword(writer, SyntaxKind.ReadonlyKeyword);
@@ -2566,8 +2556,8 @@ namespace ts {
                         writePunctuation(writer, SyntaxKind.SemicolonToken);
                         writer.writeLine();
                     }
-                    writeIndexSignature(resolved.stringIndexInfo, SyntaxKind.StringKeyword);
-                    writeIndexSignature(resolved.numberIndexInfo, SyntaxKind.NumberKeyword);
+                    buildIndexSignatureDisplay(resolved.stringIndexInfo, writer, SyntaxKind.StringKeyword, enclosingDeclaration, globalFlags, symbolStack);
+                    buildIndexSignatureDisplay(resolved.numberIndexInfo, writer, SyntaxKind.NumberKeyword, enclosingDeclaration, globalFlags, symbolStack);
                     for (const p of resolved.properties) {
                         const t = getTypeOfSymbol(p);
                         if (p.flags & (SymbolFlags.Function | SymbolFlags.Method) && !getPropertiesOfObjectType(t).length) {
@@ -2800,6 +2790,29 @@ namespace ts {
                 buildReturnTypeDisplay(signature, writer, enclosingDeclaration, flags, symbolStack);
             }
 
+            /**
+             * @param keyword The keyword for the type of IndexSignature. Must be one of SyntaxKind.NumberKeyword or SyntaxKind.StringKeyword.
+             */
+            function buildIndexSignatureDisplay(info: IndexInfo, writer: SymbolWriter, keyword: SyntaxKind, enclosingDeclaration?: Node, globalFlags?: TypeFormatFlags, symbolStack?: Symbol[]) {
+                if (info) {
+                    if (info.isReadonly) {
+                        writeKeyword(writer, SyntaxKind.ReadonlyKeyword);
+                        writeSpace(writer);
+                    }
+                    writePunctuation(writer, SyntaxKind.OpenBracketToken);
+                    writer.writeParameter(info.declaration ? declarationNameToString(info.declaration.parameters[0].name) : "x");
+                    writePunctuation(writer, SyntaxKind.ColonToken);
+                    writeSpace(writer);
+                    writeKeyword(writer, keyword);
+                    writePunctuation(writer, SyntaxKind.CloseBracketToken);
+                    writePunctuation(writer, SyntaxKind.ColonToken);
+                    writeSpace(writer);
+                    buildTypeDisplay(info.type, writer, enclosingDeclaration, globalFlags, symbolStack);
+                    writePunctuation(writer, SyntaxKind.SemicolonToken);
+                    writer.writeLine();
+                }
+            }
+
             return _displayBuilder || (_displayBuilder = {
                 buildSymbolDisplay,
                 buildTypeDisplay,
@@ -2810,6 +2823,7 @@ namespace ts {
                 buildDisplayForTypeParametersAndDelimiters,
                 buildTypeParameterDisplayFromSymbol,
                 buildSignatureDisplay,
+                buildIndexSignatureDisplay,
                 buildReturnTypeDisplay
             });
         }
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 4adf4f7ac95..eb9584f638a 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2352,6 +2352,7 @@ namespace ts {
         getTypeAtLocation(node: Node): Type;
         getTypeFromTypeReference(node: TypeReferenceNode | ExpressionWithTypeArguments | JSDocTypeReference): Type;
         signatureToString(signature: Signature, enclosingDeclaration?: Node, flags?: TypeFormatFlags, kind?: SignatureKind): string;
+        indexSignatureToString(info: IndexInfo, kind: SyntaxKind, enclosingDeclaration?: Node): string;
         typeToString(type: Type, enclosingDeclaration?: Node, flags?: TypeFormatFlags): string;
         symbolToString(symbol: Symbol, enclosingDeclaration?: Node, meaning?: SymbolFlags): string;
         createSymbol(flags: SymbolFlags, name: string): Symbol;
@@ -2396,6 +2397,7 @@ namespace ts {
         buildTypeDisplay(type: Type, writer: SymbolWriter, enclosingDeclaration?: Node, flags?: TypeFormatFlags): void;
         buildSymbolDisplay(symbol: Symbol, writer: SymbolWriter, enclosingDeclaration?: Node, meaning?: SymbolFlags, flags?: SymbolFormatFlags): void;
         buildSignatureDisplay(signatures: Signature, writer: SymbolWriter, enclosingDeclaration?: Node, flags?: TypeFormatFlags, kind?: SignatureKind): void;
+        buildIndexSignatureDisplay(info: IndexInfo, writer: SymbolWriter, keyword: SyntaxKind, enclosingDeclaration?: Node, globalFlags?: TypeFormatFlags, symbolStack?: Symbol[]): void;
         buildParameterDisplay(parameter: Symbol, writer: SymbolWriter, enclosingDeclaration?: Node, flags?: TypeFormatFlags): void;
         buildTypeParameterDisplay(tp: TypeParameter, writer: SymbolWriter, enclosingDeclaration?: Node, flags?: TypeFormatFlags): void;
         buildTypePredicateDisplay(predicate: TypePredicate, writer: SymbolWriter, enclosingDeclaration?: Node, flags?: TypeFormatFlags): void;