diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 68c9bd06825..9ad692f3b6c 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -17,7 +17,7 @@ namespace ts {
         True = -1
     }
 
-    export function createFileMap<T>(getCanonicalFileName: (fileName: string) => string): FileMap<T> {
+    export function createFileMap<T>(getCanonicalFileName: (fileName: string) => string, currentDirectory: string): FileMap<T> {
         let files: Map<T> = {};
         return {
             get,
@@ -50,7 +50,7 @@ namespace ts {
         }
 
         function normalizeKey(key: string) {
-            return getCanonicalFileName(normalizeSlashes(key));
+            return getCanonicalFileName(getNormalizedAbsolutePath(key, currentDirectory));
         }
 
         function clear() {
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index e9f659792f9..5a27aa108dc 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -346,10 +346,10 @@ namespace ts {
             ? ((moduleNames: string[], containingFile: string) => host.resolveModuleNames(moduleNames, containingFile))
             : ((moduleNames: string[], containingFile: string) => map(moduleNames, moduleName => resolveModuleName(moduleName, containingFile, options, host).resolvedModule));
 
-        let filesByName = createFileMap<SourceFile>(getCanonicalFileName);
+        let filesByName = createFileMap<SourceFile>(getCanonicalFileName, currentDirectory);
         // stores 'filename -> file association' ignoring case
         // used to track cases when two file names differ only in casing 
-        let filesByNameIgnoreCase = host.useCaseSensitiveFileNames() ? createFileMap<SourceFile>(fileName => fileName.toLowerCase()) : undefined;
+        let filesByNameIgnoreCase = host.useCaseSensitiveFileNames() ? createFileMap<SourceFile>(fileName => fileName.toLowerCase(), currentDirectory) : undefined;
 
         if (oldProgram) {
             // check properties that can affect structure of the program or module resolution strategy
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index d2e16487d07..9384244c831 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -93,8 +93,8 @@ namespace ts.server {
 
         constructor(public host: ServerHost, public project: Project) {
             const getCanonicalFileName = createGetCanonicalFileName(host.useCaseSensitiveFileNames);
-            this.resolvedModuleNames = createFileMap<Map<TimestampedResolvedModule>>(getCanonicalFileName);
-            this.filenameToScript = createFileMap<ScriptInfo>(getCanonicalFileName);
+            this.resolvedModuleNames = createFileMap<Map<TimestampedResolvedModule>>(getCanonicalFileName, host.getCurrentDirectory());
+            this.filenameToScript = createFileMap<ScriptInfo>(getCanonicalFileName, host.getCurrentDirectory());
             this.moduleResolutionHost = {
                 fileExists: fileName => this.fileExists(fileName),
                 readFile: fileName => this.host.readFile(fileName)
diff --git a/src/services/services.ts b/src/services/services.ts
index 5815e2ab1d1..dbb208be5f5 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1698,7 +1698,7 @@ namespace ts {
 
         constructor(private host: LanguageServiceHost, getCanonicalFileName: (fileName: string) => string) {
             // script id => script index
-            this.fileNameToEntry = createFileMap<HostFileInformation>(getCanonicalFileName);
+            this.fileNameToEntry = createFileMap<HostFileInformation>(getCanonicalFileName, host.getCurrentDirectory());
 
             // Initialize the list with the root file names
             let rootFileNames = host.getScriptFileNames();
@@ -1993,7 +1993,7 @@ namespace ts {
     }
 
 
-    export function createDocumentRegistry(useCaseSensitiveFileNames?: boolean): DocumentRegistry {
+    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.
         let buckets: Map<FileMap<DocumentRegistryEntry>> = {};
@@ -2007,7 +2007,7 @@ namespace ts {
             let key = getKeyFromCompilationSettings(settings);
             let bucket = lookUp(buckets, key);
             if (!bucket && createIfMissing) {
-                buckets[key] = bucket = createFileMap<DocumentRegistryEntry>(getCanonicalFileName);
+                buckets[key] = bucket = createFileMap<DocumentRegistryEntry>(getCanonicalFileName, currentDirectory);
             }
             return bucket;
         }
@@ -2556,7 +2556,9 @@ namespace ts {
         }
     }
 
-    export function createLanguageService(host: LanguageServiceHost, documentRegistry: DocumentRegistry = createDocumentRegistry()): LanguageService {
+    export function createLanguageService(host: LanguageServiceHost, 
+        documentRegistry: DocumentRegistry = createDocumentRegistry(host.useCaseSensitiveFileNames && host.useCaseSensitiveFileNames(), host.getCurrentDirectory())): LanguageService {
+
         let syntaxTreeCache: SyntaxTreeCache = new SyntaxTreeCache(host);
         let ruleProvider: formatting.RulesProvider;
         let program: Program;