diff --git a/src/compiler/builder.ts b/src/compiler/builder.ts
index b5f0339c054..b2ab858cbd4 100644
--- a/src/compiler/builder.ts
+++ b/src/compiler/builder.ts
@@ -39,7 +39,7 @@ namespace ts {
          */
         seenAffectedFiles: Map<true> | undefined;
         /**
-         * program corresponding to this state
+         * whether this program has cleaned semantic diagnostics cache for lib files
          */
         cleanedDiagnosticsOfLibFiles?: boolean;
         /**
@@ -68,9 +68,11 @@ namespace ts {
             state.semanticDiagnosticsPerFile = createMap<ReadonlyArray<Diagnostic>>();
         }
         state.changedFilesSet = createMap<true>();
+
         const useOldState = BuilderState.canReuseOldState(state.referencedMap, oldState);
+        const oldCompilerOptions = useOldState ? oldState!.program.getCompilerOptions() : undefined;
         const canCopySemanticDiagnostics = useOldState && oldState!.semanticDiagnosticsPerFile && !!state.semanticDiagnosticsPerFile &&
-            !compilerOptionsAffectSemanticDiagnostics(compilerOptions, oldState!.program.getCompilerOptions());
+            !compilerOptionsAffectSemanticDiagnostics(compilerOptions, oldCompilerOptions!);
         if (useOldState) {
             // Verify the sanity of old state
             if (!oldState!.currentChangedFilePath) {
@@ -87,8 +89,8 @@ namespace ts {
         // Update changed files and copy semantic diagnostics if we can
         const referencedMap = state.referencedMap;
         const oldReferencedMap = useOldState ? oldState!.referencedMap : undefined;
-        const copyDeclarationFileDiagnostics = canCopySemanticDiagnostics && !compilerOptions.skipLibCheck === !oldState!.program.getCompilerOptions().skipLibCheck;
-        const copyLibFileDiagnostics = copyDeclarationFileDiagnostics && !compilerOptions.skipDefaultLibCheck === !oldState!.program.getCompilerOptions().skipDefaultLibCheck;
+        const copyDeclarationFileDiagnostics = canCopySemanticDiagnostics && !compilerOptions.skipLibCheck === !oldCompilerOptions!.skipLibCheck;
+        const copyLibFileDiagnostics = copyDeclarationFileDiagnostics && !compilerOptions.skipDefaultLibCheck === !oldCompilerOptions!.skipDefaultLibCheck;
         state.fileInfos.forEach((info, sourceFilePath) => {
             let oldInfo: Readonly<BuilderState.FileInfo> | undefined;
             let newReferences: BuilderState.ReferencedSet | undefined;
@@ -209,7 +211,7 @@ namespace ts {
             state.cleanedDiagnosticsOfLibFiles = true;
             const options = state.program.getCompilerOptions();
             if (forEach(state.program.getSourceFiles(), f =>
-                !contains(state.allFilesExcludingDefaultLibraryFile, f) &&
+                state.program.isSourceFileDefaultLibrary(f) &&
                 !skipTypeChecking(f, options) &&
                 removeSemanticDiagnosticsOf(state, f.path)
             )) {