diff --git a/build/lib/tsb/transpiler.js b/build/lib/tsb/transpiler.js
index 7da255d529f..38e6b5c00e4 100644
--- a/build/lib/tsb/transpiler.js
+++ b/build/lib/tsb/transpiler.js
@@ -121,20 +121,29 @@ class Transpiler {
         this._allJobs = [];
         logFn('Transpile', `will use ${Transpiler.P} transpile worker`);
         this._getOutputFileName = (file) => {
-            if (!_cmdLine.options.configFilePath) {
-                // this is needed for the INTERNAL getOutputFileNames-call below...
-                _cmdLine.options.configFilePath = configFilePath;
+            try {
+                // windows: path-sep normalizing
+                file = ts.normalizePath(file);
+                if (!_cmdLine.options.configFilePath) {
+                    // this is needed for the INTERNAL getOutputFileNames-call below...
+                    _cmdLine.options.configFilePath = configFilePath;
+                }
+                const isDts = file.endsWith('.d.ts');
+                if (isDts) {
+                    file = file.slice(0, -5) + '.ts';
+                    _cmdLine.fileNames.push(file);
+                }
+                const outfile = ts.getOutputFileNames(_cmdLine, file, true)[0];
+                if (isDts) {
+                    _cmdLine.fileNames.pop();
+                }
+                return outfile;
             }
-            const isDts = file.endsWith('.d.ts');
-            if (isDts) {
-                file = file.slice(0, -5) + '.ts';
-                _cmdLine.fileNames.push(file);
+            catch (err) {
+                console.error(file, _cmdLine.fileNames);
+                console.error(err);
+                throw new err;
             }
-            const outfile = ts.getOutputFileNames(_cmdLine, file, true)[0];
-            if (isDts) {
-                _cmdLine.fileNames.pop();
-            }
-            return outfile;
         };
     }
     async join() {
diff --git a/build/lib/tsb/transpiler.ts b/build/lib/tsb/transpiler.ts
index 3afc3547dd5..7bd789ef6eb 100644
--- a/build/lib/tsb/transpiler.ts
+++ b/build/lib/tsb/transpiler.ts
@@ -166,23 +166,35 @@ export class Transpiler {
 		// very complicated logic to re-use TS internal functions to know the output path
 		// given a TS input path and its config
 		type InternalTsApi = typeof ts & {
+			normalizePath(path: string): string;
 			getOutputFileNames(commandLine: ts.ParsedCommandLine, inputFileName: string, ignoreCase: boolean): readonly string[];
 		};
 		this._getOutputFileName = (file) => {
-			if (!_cmdLine.options.configFilePath) {
-				// this is needed for the INTERNAL getOutputFileNames-call below...
-				_cmdLine.options.configFilePath = configFilePath;
+			try {
+
+				// windows: path-sep normalizing
+				file = (<InternalTsApi>ts).normalizePath(file);
+
+				if (!_cmdLine.options.configFilePath) {
+					// this is needed for the INTERNAL getOutputFileNames-call below...
+					_cmdLine.options.configFilePath = configFilePath;
+				}
+				const isDts = file.endsWith('.d.ts');
+				if (isDts) {
+					file = file.slice(0, -5) + '.ts';
+					_cmdLine.fileNames.push(file);
+				}
+				const outfile = (<InternalTsApi>ts).getOutputFileNames(_cmdLine, file, true)[0];
+				if (isDts) {
+					_cmdLine.fileNames.pop();
+				}
+				return outfile;
+
+			} catch (err) {
+				console.error(file, _cmdLine.fileNames);
+				console.error(err);
+				throw new err;
 			}
-			const isDts = file.endsWith('.d.ts');
-			if (isDts) {
-				file = file.slice(0, -5) + '.ts';
-				_cmdLine.fileNames.push(file);
-			}
-			const outfile = (<InternalTsApi>ts).getOutputFileNames(_cmdLine, file, true)[0];
-			if (isDts) {
-				_cmdLine.fileNames.pop();
-			}
-			return outfile;
 		};
 	}