diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index aba2e48e4a1..639660a2a4c 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -872,4 +872,11 @@ namespace ts {
         }
         return copiedList;
     }
+
+    export function createGetCanonicalFileName(useCaseSensitivefileNames: boolean): (fileName: string) => string {
+        return useCaseSensitivefileNames
+            ? ((fileName) => fileName)
+            : ((fileName) => fileName.toLowerCase());
+    }
+
 }
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 073a662ce1c..e6f908d250a 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -11,7 +11,7 @@ namespace ts {
         write(s: string): void;
         readFile(path: string, encoding?: string): string;
         writeFile(path: string, data: string, writeByteOrderMark?: boolean): void;
-        watchFile?(path: string, callback: FileWatcherCallback): FileWatcher;
+        watchFile?(path: Path, callback: FileWatcherCallback): FileWatcher;
         watchDirectory?(path: string, callback: DirectoryWatcherCallback, recursive?: boolean): FileWatcher;
         resolvePath(path: string): string;
         fileExists(path: string): boolean;
@@ -500,13 +500,13 @@ namespace ts {
                 },
                 readFile,
                 writeFile,
-                watchFile: (fileName, callback) => {
+                watchFile: (filePath, callback) => {
                     // Node 4.0 stablized the `fs.watch` function on Windows which avoids polling
                     // and is more efficient than `fs.watchFile` (ref: https://github.com/nodejs/node/pull/2649
                     // and https://github.com/Microsoft/TypeScript/issues/4643), therefore
                     // if the current node.js version is newer than 4, use `fs.watch` instead.
                     const watchSet = isNode4OrLater() ? watchedFileSet : pollingWatchedFileSet;
-                    const watchedFile =  watchSet.addFile(<Path>fileName, callback);
+                    const watchedFile =  watchSet.addFile(filePath, callback);
                     return {
                         close: () => watchSet.removeFile(watchedFile)
                     };
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index d064ec54c9c..808ee6da804 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -334,7 +334,8 @@ namespace ts {
                 return sys.exit(ExitStatus.DiagnosticsPresent_OutputsSkipped);
             }
             if (configFileName) {
-                configFileWatcher = sys.watchFile(configFileName, configFileChanged);
+                const configFilePath = toPath(configFileName, sys.getCurrentDirectory(), createGetCanonicalFileName(sys.useCaseSensitiveFileNames));
+                configFileWatcher = sys.watchFile(configFilePath, configFileChanged);
             }
             if (sys.watchDirectory && configFileName) {
                 const directory = ts.getDirectoryPath(configFileName);
@@ -442,7 +443,8 @@ namespace ts {
             const sourceFile = hostGetSourceFile(fileName, languageVersion, onError);
             if (sourceFile && compilerOptions.watch) {
                 // Attach a file watcher
-                sourceFile.fileWatcher = sys.watchFile(sourceFile.fileName, (fileName: string, removed?: boolean) => sourceFileChanged(sourceFile, removed));
+                const filePath = toPath(sourceFile.fileName, sys.getCurrentDirectory(), createGetCanonicalFileName(sys.useCaseSensitiveFileNames));
+                sourceFile.fileWatcher = sys.watchFile(filePath, (fileName: string, removed?: boolean) => sourceFileChanged(sourceFile, removed));
             }
             return sourceFile;
         }
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 5a1c85fc13c..0442575aded 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -1000,7 +1000,7 @@ namespace ts.server {
                     info.setFormatOptions(this.getFormatCodeOptions());
                     this.filenameToScriptInfo[fileName] = info;
                     if (!info.isOpen) {
-                        info.fileWatcher = this.host.watchFile(fileName, _ => { this.watchedFileChanged(fileName); });
+                        info.fileWatcher = this.host.watchFile(<Path>fileName, _ => { this.watchedFileChanged(fileName); });
                     }
                 }
             }
@@ -1213,7 +1213,7 @@ namespace ts.server {
                     }
                 }
                 project.finishGraph();
-                project.projectFileWatcher = this.host.watchFile(configFilename, _ => this.watchedProjectConfigFileChanged(project));
+                project.projectFileWatcher = this.host.watchFile(<Path>configFilename, _ => this.watchedProjectConfigFileChanged(project));
                 this.log("Add recursive watcher for: " + ts.getDirectoryPath(configFilename));
                 project.directoryWatcher = this.host.watchDirectory(
                     ts.getDirectoryPath(configFilename),
diff --git a/src/services/services.ts b/src/services/services.ts
index 0ffd1138cba..0f3c18f7a85 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -2008,13 +2008,6 @@ namespace ts {
         return createLanguageServiceSourceFile(sourceFile.fileName, scriptSnapshot, sourceFile.languageVersion, version, /*setNodeParents*/ true);
     }
 
-    export function createGetCanonicalFileName(useCaseSensitivefileNames: boolean): (fileName: string) => string {
-        return useCaseSensitivefileNames
-            ? ((fileName) => fileName)
-            : ((fileName) => fileName.toLowerCase());
-    }
-
-
     export function createDocumentRegistry(useCaseSensitiveFileNames?: boolean, currentDirectory = ""): DocumentRegistry {
         // Maps from compiler setting target (ES3, ES5, etc.) to all the cached documents we have
         // for those settings.