diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2650e50a04e..ba85e090265 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2172,8 +2172,7 @@ namespace ts {
                 return;
             }
             const host = getJSDocHost(node);
-            if (host &&
-                isExpressionStatement(host) &&
+            if (isExpressionStatement(host) &&
                 isBinaryExpression(host.expression) &&
                 getSpecialPropertyAssignmentKind(host.expression) === SpecialPropertyAssignmentKind.PrototypeProperty) {
                 const symbol = getSymbolOfNode(host.expression.left);
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index fa6f65640da..300c6421dbc 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1927,11 +1927,7 @@ namespace ts {
     }
 
     export function getJSDocHost(node: Node): HasJSDoc {
-        const comment = findAncestor(node.parent,
-            node => !(isJSDocNode(node) || node.flags & NodeFlags.JSDoc) ? "quit" : node.kind === SyntaxKind.JSDocComment);
-        if (comment) {
-            return (comment as JSDoc).parent;
-        }
+        return Debug.assertDefined(findAncestor(node.parent, isJSDoc)).parent;
     }
 
     export function getTypeParameterFromJsDoc(node: TypeParameterDeclaration & { parent: JSDocTemplateTag }): TypeParameterDeclaration | undefined {