diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index cde61bb4071e7..8eb6f2b13f475 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -250,6 +250,7 @@ namespace ts {
             getSuggestionForNonexistentProperty: (node, type) => getSuggestionForNonexistentProperty(node, type),
             getSuggestionForNonexistentSymbol: (location, name, meaning) => getSuggestionForNonexistentSymbol(location, escapeLeadingUnderscores(name), meaning),
             getBaseConstraintOfType,
+            getDefaultFromTypeParameter: type => type && type.flags & TypeFlags.TypeParameter ? getDefaultFromTypeParameter(type as TypeParameter) : undefined,
             resolveName(name, location, meaning) {
                 return resolveName(location, escapeLeadingUnderscores(name), meaning, /*nameNotFoundMessage*/ undefined, /*nameArg*/ undefined, /*isUse*/ false);
             },
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 26148a0b2f191..82f66e7727871 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2766,7 +2766,8 @@ namespace ts {
         getApparentType(type: Type): Type;
         getSuggestionForNonexistentProperty(node: Identifier, containingType: Type): string | undefined;
         getSuggestionForNonexistentSymbol(location: Node, name: string, meaning: SymbolFlags): string | undefined;
-        /* @internal */ getBaseConstraintOfType(type: Type): Type | undefined;
+        getBaseConstraintOfType(type: Type): Type | undefined;
+        getDefaultFromTypeParameter(type: Type): Type | undefined;
 
         /* @internal */ getAnyType(): Type;
         /* @internal */ getStringType(): Type;
@@ -3570,15 +3571,17 @@ namespace ts {
 
     export interface TypeVariable extends Type {
         /* @internal */
-        resolvedBaseConstraint: Type;
+        resolvedBaseConstraint?: Type;
         /* @internal */
-        resolvedIndexType: IndexType;
+        resolvedIndexType?: IndexType;
     }
 
     // Type parameters (TypeFlags.TypeParameter)
     export interface TypeParameter extends TypeVariable {
         /** Retrieve using getConstraintFromTypeParameter */
-        constraint: Type;        // Constraint
+        /* @internal */
+        constraint?: Type;        // Constraint
+        /* @internal */
         default?: Type;
         /* @internal */
         target?: TypeParameter;  // Instantiation target
diff --git a/src/services/services.ts b/src/services/services.ts
index d62fc88a649d0..0d5e468031231 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -472,6 +472,12 @@ namespace ts {
         getNonNullableType(): Type {
             return this.checker.getNonNullableType(this);
         }
+        getConstraint(): Type | undefined {
+            return this.checker.getBaseConstraintOfType(this);
+        }
+        getDefault(): Type | undefined {
+            return this.checker.getDefaultFromTypeParameter(this);
+        }
     }
 
     class SignatureObject implements Signature {
diff --git a/src/services/types.ts b/src/services/types.ts
index 28de0566a500b..e74b830cc45c9 100644
--- a/src/services/types.ts
+++ b/src/services/types.ts
@@ -50,6 +50,8 @@ namespace ts {
         getNumberIndexType(): Type | undefined;
         getBaseTypes(): BaseType[] | undefined;
         getNonNullableType(): Type;
+        getConstraint(): Type | undefined;
+        getDefault(): Type | undefined;
     }
 
     export interface Signature {
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index d3a97c756902b..d322e04893e0c 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -1779,6 +1779,8 @@ declare namespace ts {
         getApparentType(type: Type): Type;
         getSuggestionForNonexistentProperty(node: Identifier, containingType: Type): string | undefined;
         getSuggestionForNonexistentSymbol(location: Node, name: string, meaning: SymbolFlags): string | undefined;
+        getBaseConstraintOfType(type: Type): Type | undefined;
+        getDefaultFromTypeParameter(type: Type): Type | undefined;
     }
     enum NodeBuilderFlags {
         None = 0,
@@ -2115,9 +2117,6 @@ declare namespace ts {
     interface TypeVariable extends Type {
     }
     interface TypeParameter extends TypeVariable {
-        /** Retrieve using getConstraintFromTypeParameter */
-        constraint: Type;
-        default?: Type;
     }
     interface IndexedAccessType extends TypeVariable {
         objectType: Type;
@@ -3838,6 +3837,8 @@ declare namespace ts {
         getNumberIndexType(): Type | undefined;
         getBaseTypes(): BaseType[] | undefined;
         getNonNullableType(): Type;
+        getConstraint(): Type | undefined;
+        getDefault(): Type | undefined;
     }
     interface Signature {
         getDeclaration(): SignatureDeclaration;
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 43b668fe2d1a1..17c75ed0336f1 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -1779,6 +1779,8 @@ declare namespace ts {
         getApparentType(type: Type): Type;
         getSuggestionForNonexistentProperty(node: Identifier, containingType: Type): string | undefined;
         getSuggestionForNonexistentSymbol(location: Node, name: string, meaning: SymbolFlags): string | undefined;
+        getBaseConstraintOfType(type: Type): Type | undefined;
+        getDefaultFromTypeParameter(type: Type): Type | undefined;
     }
     enum NodeBuilderFlags {
         None = 0,
@@ -2115,9 +2117,6 @@ declare namespace ts {
     interface TypeVariable extends Type {
     }
     interface TypeParameter extends TypeVariable {
-        /** Retrieve using getConstraintFromTypeParameter */
-        constraint: Type;
-        default?: Type;
     }
     interface IndexedAccessType extends TypeVariable {
         objectType: Type;
@@ -3838,6 +3837,8 @@ declare namespace ts {
         getNumberIndexType(): Type | undefined;
         getBaseTypes(): BaseType[] | undefined;
         getNonNullableType(): Type;
+        getConstraint(): Type | undefined;
+        getDefault(): Type | undefined;
     }
     interface Signature {
         getDeclaration(): SignatureDeclaration;