diff --git a/src/compiler/builder.ts b/src/compiler/builder.ts
index 68d3796fa345d..c63627df3e60b 100644
--- a/src/compiler/builder.ts
+++ b/src/compiler/builder.ts
@@ -705,9 +705,11 @@ namespace ts {
         return filterSemanticDiagnotics(diagnostics, state.compilerOptions);
     }
 
-    export type ProgramBuildInfoDiagnostic = number | [fileId: number, diagnostics: readonly ReusableDiagnostic[]];
-    export type ProgramBuilderInfoFilePendingEmit = [fileId: number, emitKind: BuilderFileEmit];
-    export type ProgramBuildInfoReferencedMap = [fileId: number, fileIdListId: number][];
+    export type ProgramBuildInfoFileId = number & { __programBuildInfoFileIdBrand: any };
+    export type ProgramBuildInfoFileIdListId = number & { __programBuildInfoFileIdListIdBrand: any };
+    export type ProgramBuildInfoDiagnostic = ProgramBuildInfoFileId | [fileId: ProgramBuildInfoFileId, diagnostics: readonly ReusableDiagnostic[]];
+    export type ProgramBuilderInfoFilePendingEmit = [fileId: ProgramBuildInfoFileId, emitKind: BuilderFileEmit];
+    export type ProgramBuildInfoReferencedMap = [fileId: ProgramBuildInfoFileId, fileIdListId: ProgramBuildInfoFileIdListId][];
     export type ProgramBuildInfoBuilderStateFileInfo = Omit<BuilderState.FileInfo, "signature"> & {
         /**
          * Signature is
@@ -725,7 +727,7 @@ namespace ts {
         fileNames: readonly string[];
         fileInfos: readonly ProgramBuildInfoFileInfo[];
         options: CompilerOptions | undefined;
-        fileIdsList?: readonly (readonly number[])[];
+        fileIdsList?: readonly (readonly ProgramBuildInfoFileId[])[];
         referencedMap?: ProgramBuildInfoReferencedMap;
         exportedModulesMap?: ProgramBuildInfoReferencedMap;
         semanticDiagnosticsPerFile?: ProgramBuildInfoDiagnostic[];
@@ -740,9 +742,9 @@ namespace ts {
         const currentDirectory = Debug.checkDefined(state.program).getCurrentDirectory();
         const buildInfoDirectory = getDirectoryPath(getNormalizedAbsolutePath(getTsBuildInfoEmitOutputFilePath(state.compilerOptions)!, currentDirectory));
         const fileNames: string[] = [];
-        const fileNameToFileId = new Map<string, number>();
-        let fileIdsList: (readonly number[])[] | undefined;
-        let fileNamesToFileIdListId: ESMap<string, number> | undefined;
+        const fileNameToFileId = new Map<string, ProgramBuildInfoFileId>();
+        let fileIdsList: (readonly ProgramBuildInfoFileId[])[] | undefined;
+        let fileNamesToFileIdListId: ESMap<string, ProgramBuildInfoFileIdListId> | undefined;
         const fileInfos = arrayFrom(state.fileInfos.entries(), ([key, value]): ProgramBuildInfoFileInfo => {
             // Ensure fileId
             const fileId = toFileId(key);
@@ -825,22 +827,22 @@ namespace ts {
             return ensurePathIsNonModuleName(getRelativePathFromDirectory(buildInfoDirectory, path, getCanonicalFileName));
         }
 
-        function toFileId(path: Path): number {
+        function toFileId(path: Path): ProgramBuildInfoFileId {
             let fileId = fileNameToFileId.get(path);
             if (fileId === undefined) {
                 fileNames.push(relativeToBuildInfo(path));
-                fileNameToFileId.set(path, fileId = fileNames.length);
+                fileNameToFileId.set(path, fileId = fileNames.length as ProgramBuildInfoFileId);
             }
             return fileId;
         }
 
-        function toFileIdListId(set: ReadonlySet<Path>): number {
+        function toFileIdListId(set: ReadonlySet<Path>): ProgramBuildInfoFileIdListId {
             const fileIds = arrayFrom(set.keys(), toFileId).sort(compareValues);
             const key = fileIds.join();
             let fileIdListId = fileNamesToFileIdListId?.get(key);
             if (fileIdListId === undefined) {
                 (fileIdsList ||= []).push(fileIds);
-                (fileNamesToFileIdListId ||= new Map()).set(key, fileIdListId = fileIdsList.length);
+                (fileNamesToFileIdListId ||= new Map()).set(key, fileIdListId = fileIdsList.length as ProgramBuildInfoFileIdListId);
             }
             return fileIdListId;
         }
@@ -1249,7 +1251,7 @@ namespace ts {
         const filePaths = program.fileNames.map(toPath);
         const filePathsSetList = program.fileIdsList?.map(fileIds => new Set(fileIds.map(toFilePath)));
         const fileInfos = new Map<Path, BuilderState.FileInfo>();
-        program.fileInfos.forEach((fileInfo, index) => fileInfos.set(toFilePath(index + 1), toBuilderStateFileInfo(fileInfo)));
+        program.fileInfos.forEach((fileInfo, index) => fileInfos.set(toFilePath(index + 1 as ProgramBuildInfoFileId), toBuilderStateFileInfo(fileInfo)));
         const state: ReusableBuilderProgramState = {
             fileInfos,
             compilerOptions: program.options ? convertToOptionsWithAbsolutePaths(program.options, toAbsolutePath) : {},
@@ -1294,11 +1296,11 @@ namespace ts {
             return getNormalizedAbsolutePath(path, buildInfoDirectory);
         }
 
-        function toFilePath(fileId: number) {
+        function toFilePath(fileId: ProgramBuildInfoFileId) {
             return filePaths[fileId - 1];
         }
 
-        function toFilePathsSet(fileIdsListId: number) {
+        function toFilePathsSet(fileIdsListId: ProgramBuildInfoFileIdListId) {
             return filePathsSetList![fileIdsListId - 1];
         }
 
diff --git a/src/testRunner/unittests/tsbuild/helpers.ts b/src/testRunner/unittests/tsbuild/helpers.ts
index 776ef9fcb062e..05800deaaac4f 100644
--- a/src/testRunner/unittests/tsbuild/helpers.ts
+++ b/src/testRunner/unittests/tsbuild/helpers.ts
@@ -236,24 +236,24 @@ interface Symbol {
         }
     }
 
-    type ProgramBuildInfoDiagnostic = string | [string, readonly ReusableDiagnostic[]];
-    type ProgramBuilderInfoFilePendingEmit = [string, "DtsOnly" | "Full"];
-    interface ProgramBuildInfo {
+    type ReadableProgramBuildInfoDiagnostic = string | [string, readonly ReusableDiagnostic[]];
+    type ReadableProgramBuilderInfoFilePendingEmit = [string, "DtsOnly" | "Full"];
+    interface ReadableProgramBuildInfo {
         fileNames: readonly string[];
         fileNamesList: readonly (readonly string[])[] | undefined;
         fileInfos: MapLike<BuilderState.FileInfo>;
         options: CompilerOptions | undefined;
         referencedMap?: MapLike<string[]>;
         exportedModulesMap?: MapLike<string[]>;
-        semanticDiagnosticsPerFile?: readonly ProgramBuildInfoDiagnostic[];
-        affectedFilesPendingEmit?: readonly ProgramBuilderInfoFilePendingEmit[];
+        semanticDiagnosticsPerFile?: readonly ReadableProgramBuildInfoDiagnostic[];
+        affectedFilesPendingEmit?: readonly ReadableProgramBuilderInfoFilePendingEmit[];
     }
-    type ReadableBuildInfo = Omit<BuildInfo, "program"> & { program: ProgramBuildInfo | undefined; size: number; };
+    type ReadableBuildInfo = Omit<BuildInfo, "program"> & { program: ReadableProgramBuildInfo | undefined; size: number; };
     function generateBuildInfoProgramBaseline(sys: System, originalWriteFile: System["writeFile"], buildInfoPath: string, buildInfo: BuildInfo) {
-        const fileInfos: ProgramBuildInfo["fileInfos"] = {};
-        buildInfo.program?.fileInfos.forEach((fileInfo, index) => fileInfos[toFileName(index + 1)] = toBuilderStateFileInfo(fileInfo));
+        const fileInfos: ReadableProgramBuildInfo["fileInfos"] = {};
+        buildInfo.program?.fileInfos.forEach((fileInfo, index) => fileInfos[toFileName(index + 1 as ProgramBuildInfoFileId)] = toBuilderStateFileInfo(fileInfo));
         const fileNamesList = buildInfo.program?.fileIdsList?.map(fileIdsListId => fileIdsListId.map(toFileName));
-        const program: ProgramBuildInfo | undefined = buildInfo.program && {
+        const program: ReadableProgramBuildInfo | undefined = buildInfo.program && {
             fileNames: buildInfo.program.fileNames,
             fileNamesList,
             fileInfos,
@@ -282,11 +282,11 @@ interface Symbol {
         // For now its just JSON.stringify
         originalWriteFile.call(sys, `${buildInfoPath}.readable.baseline.txt`, JSON.stringify(result, /*replacer*/ undefined, 2));
 
-        function toFileName(fileId: number) {
+        function toFileName(fileId: ProgramBuildInfoFileId) {
             return buildInfo.program!.fileNames[fileId - 1];
         }
 
-        function toFileNames(fileIdsListId: number) {
+        function toFileNames(fileIdsListId: ProgramBuildInfoFileIdListId) {
             return fileNamesList![fileIdsListId - 1];
         }