diff --git a/packages/compiler-cli/src/ngtsc/annotations/src/directive.ts b/packages/compiler-cli/src/ngtsc/annotations/src/directive.ts
index ce32ab2feb..e67d5bce2b 100644
--- a/packages/compiler-cli/src/ngtsc/annotations/src/directive.ts
+++ b/packages/compiler-cli/src/ngtsc/annotations/src/directive.ts
@@ -156,7 +156,7 @@ export function extractDirectiveMetadata(
     inputs: {...inputsFromMeta, ...inputsFromFields},
     outputs: {...outputsFromMeta, ...outputsFromFields}, queries, selector,
     type: new WrappedNodeExpr(clazz.name !),
-    typeArgumentCount: (clazz.typeParameters || []).length,
+    typeArgumentCount: reflector.getGenericArityOfClass(clazz) || 0,
     typeSourceSpan: null !, usesInheritance, exportAs,
   };
   return {decoratedElements, decorator: directive, metadata};
diff --git a/packages/compiler-cli/src/ngtsc/host/src/reflection.ts b/packages/compiler-cli/src/ngtsc/host/src/reflection.ts
index 21f4efede4..bb205a125d 100644
--- a/packages/compiler-cli/src/ngtsc/host/src/reflection.ts
+++ b/packages/compiler-cli/src/ngtsc/host/src/reflection.ts
@@ -411,4 +411,12 @@ export interface ReflectionHost {
   isClass(node: ts.Node): boolean;
 
   hasBaseClass(node: ts.Declaration): boolean;
+
+  /**
+   * Get the number of generic type parameters of a given class.
+   *
+   * @returns the number of type parameters of the class, if known, or `null` if the declaration
+   * is not a class or has an unknown number of type parameters.
+   */
+  getGenericArityOfClass(clazz: ts.Declaration): number|null;
 }
diff --git a/packages/compiler-cli/src/ngtsc/metadata/src/reflector.ts b/packages/compiler-cli/src/ngtsc/metadata/src/reflector.ts
index 608dde3c3a..d03bdbd26e 100644
--- a/packages/compiler-cli/src/ngtsc/metadata/src/reflector.ts
+++ b/packages/compiler-cli/src/ngtsc/metadata/src/reflector.ts
@@ -159,6 +159,13 @@ export class TypeScriptReflectionHost implements ReflectionHost {
     };
   }
 
+  getGenericArityOfClass(clazz: ts.Declaration): number|null {
+    if (!ts.isClassDeclaration(clazz)) {
+      return null;
+    }
+    return clazz.typeParameters !== undefined ? clazz.typeParameters.length : 0;
+  }
+
   /**
    * Resolve a `ts.Symbol` to its declaration, keeping track of the `viaModule` along the way.
    *
diff --git a/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts b/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
index c3808a60d9..a0988a5e37 100644
--- a/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
+++ b/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
@@ -17,7 +17,7 @@ import * as ts from 'typescript';
 
 import {ClassMemberKind, ReflectionHost} from '../../host';
 
-const TS_DTS_EXTENSION = /(\.d)?\.ts$/;
+const TS_DTS_JS_EXTENSION = /(\.d)?\.ts|\.js$/;
 
 /**
  * Represents a value which cannot be determined statically.
@@ -147,7 +147,7 @@ export class ResolvedReference<T extends ts.Node = ts.Node> extends Reference<T>
       // TODO(alxhub): investigate the need to map such paths via the Host for proper g3 support.
       let relative =
           path.posix.relative(path.dirname(context.fileName), this.node.getSourceFile().fileName)
-              .replace(TS_DTS_EXTENSION, '');
+              .replace(TS_DTS_JS_EXTENSION, '');
 
       // path.relative() does not include the leading './'.
       if (!relative.startsWith('.')) {