diff --git a/packages/language-service/src/language_service.ts b/packages/language-service/src/language_service.ts
index 92e6dd2eba5119..05055d6acde972 100644
--- a/packages/language-service/src/language_service.ts
+++ b/packages/language-service/src/language_service.ts
@@ -83,17 +83,12 @@ export class LanguageService {
 
   getSemanticDiagnostics(fileName: string): ts.Diagnostic[] {
     return this.withCompilerAndPerfTracing(PerfPhase.LsDiagnostics, (compiler) => {
-      const diagnostics: ts.Diagnostic[] = [];
+      let diagnostics: ts.Diagnostic[] = [];
       if (isTypeScriptFile(fileName)) {
         const program = compiler.getCurrentProgram();
         const sourceFile = program.getSourceFile(fileName);
         if (sourceFile) {
           let ngDiagnostics = compiler.getDiagnosticsForFile(sourceFile, OptimizeFor.SingleFile);
-          if (this.config.suppressAngularDiagnosticCodes) {
-            ngDiagnostics = ngDiagnostics.filter(
-              (diag) => !this.config.suppressAngularDiagnosticCodes!.includes(diag.code),
-            );
-          }
           // There are several kinds of diagnostics returned by `NgCompiler` for a source file:
           //
           // 1. Angular-related non-template diagnostics from decorated classes within that
@@ -130,6 +125,11 @@ export class LanguageService {
           }
         }
       }
+      if (this.config.suppressAngularDiagnosticCodes) {
+        diagnostics = diagnostics.filter(
+          (diag) => !this.config.suppressAngularDiagnosticCodes!.includes(diag.code),
+        );
+      }
       return diagnostics;
     });
   }