diff --git a/src/angular/metadataReader.ts b/src/angular/metadataReader.ts
index 9553df141..06d659e64 100644
--- a/src/angular/metadataReader.ts
+++ b/src/angular/metadataReader.ts
@@ -97,9 +97,9 @@ export class MetadataReader {
     const name = nameExpression && isStringLiteralLike(nameExpression) ? nameExpression.text : undefined;
 
     const pureExpression = getDecoratorPropertyInitializer(dec, 'pure');
-    const isBoolean = pureExpression && isBooleanLiteralLike(pureExpression);
+    const pure = pureExpression && isBooleanLiteralLike(pureExpression) ? pureExpression : undefined;
 
-    return new PipeMetadata(d, dec, name, isBoolean ? (pureExpression as ts.BooleanLiteral) : undefined);
+    return new PipeMetadata(d, dec, name, pure);
   }
 
   protected readModuleMetadata(d: ts.ClassDeclaration, dec: ts.Decorator): DirectiveMetadata {
diff --git a/src/noPipeImpureRule.ts b/src/noPipeImpureRule.ts
index 428ca7a48..0d0fca0a1 100644
--- a/src/noPipeImpureRule.ts
+++ b/src/noPipeImpureRule.ts
@@ -38,8 +38,7 @@ export class ClassMetadataWalker extends NgWalker {
   }
 
   private validatePipe(metadata: PipeMetadata): void {
-    if (!metadata.pure) return;
-    if (metadata.pure!.kind !== SyntaxKind.FalseKeyword) return;
+    if (!metadata.pure || metadata.pure.kind !== SyntaxKind.FalseKeyword) return;
 
     const className = getClassName(metadata.controller)!;