diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index c1366745c3..e7d26d1eab 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -249,7 +249,7 @@ namespace ts {
                 getTypeOfSymbol,
                 getResolvedSymbol,
                 getIndexTypeOfStructuredType,
-                getConstraintFromTypeParameter,
+                getConstraintOfTypeParameter,
                 getFirstIdentifier,
             ),
             getAmbientModules,
@@ -6951,21 +6951,12 @@ namespace ts {
             return undefined;
         }
 
-        function getBaseConstraintOfInstantiableNonPrimitiveUnionOrIntersection(type: Type) {
+        function getBaseConstraintOfType(type: Type): Type | undefined {
             if (type.flags & (TypeFlags.InstantiableNonPrimitive | TypeFlags.UnionOrIntersection)) {
                 const constraint = getResolvedBaseConstraint(<InstantiableType | UnionOrIntersectionType>type);
-                if (constraint !== noConstraintType && constraint !== circularConstraintType) {
-                    return constraint;
-                }
+                return constraint !== noConstraintType && constraint !== circularConstraintType ? constraint : undefined;
             }
-        }
-
-        function getBaseConstraintOfType(type: Type): Type | undefined {
-            const constraint = getBaseConstraintOfInstantiableNonPrimitiveUnionOrIntersection(type);
-            if (!constraint && type.flags & TypeFlags.Index) {
-                return keyofConstraintType;
-            }
-            return constraint;
+            return type.flags & TypeFlags.Index ? keyofConstraintType : undefined;
         }
 
         /**
diff --git a/src/compiler/symbolWalker.ts b/src/compiler/symbolWalker.ts
index cce6739d35..1f6930076b 100644
--- a/src/compiler/symbolWalker.ts
+++ b/src/compiler/symbolWalker.ts
@@ -9,7 +9,7 @@ namespace ts {
         getTypeOfSymbol: (sym: Symbol) => Type,
         getResolvedSymbol: (node: Node) => Symbol,
         getIndexTypeOfStructuredType: (type: Type, kind: IndexKind) => Type | undefined,
-        getConstraintFromTypeParameter: (typeParameter: TypeParameter) => Type | undefined,
+        getConstraintOfTypeParameter: (typeParameter: TypeParameter) => Type | undefined,
         getFirstIdentifier: (node: EntityNameOrEntityNameExpression) => Identifier) {
 
         return getSymbolWalker;
@@ -93,7 +93,7 @@ namespace ts {
             }
 
             function visitTypeParameter(type: TypeParameter): void {
-                visitType(getConstraintFromTypeParameter(type));
+                visitType(getConstraintOfTypeParameter(type));
             }
 
             function visitUnionOrIntersectionType(type: UnionOrIntersectionType): void {