diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0aabf861c3..e4ac83fd65 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5372,7 +5372,7 @@ namespace ts {
             while (i > 0) {
                 i--;
                 if (isSubtypeOfAny(types[i], types)) {
-                    removeItemAtPreservingOrder(types, i);
+                    orderedRemoveItemAt(types, i);
                 }
             }
         }
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index b09288e63d..9a951243e0 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1501,7 +1501,7 @@ namespace ts {
     }
 
     /** Remove an item from an array, moving everything to its right one space left. */
-    export function removeItemAtPreservingOrder<T>(array: T[], index: number): void {
+    export function orderedRemoveItemAt<T>(array: T[], index: number): void {
         // This seems to be faster than either `array.splice(i, 1)` or `array.copyWithin(i, i+ 1)`.
         for (let i = index; i < array.length - 1; i++) {
             array[i] = array[i + 1];
@@ -1516,7 +1516,7 @@ namespace ts {
     }
 
     /** Remove the *first* occurrence of `item` from the array. */
-    export function unorderedRemoveItem<T>(item: T, array: T[]): void {
+    export function unorderedRemoveItem<T>(array: T[], item: T): void {
         unorderedRemoveFirstItemWhere(array, element => element === item);
     }
 
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 966a282ae6..118186bf52 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -285,7 +285,7 @@ namespace ts {
                 function removeFileWatcherCallback(filePath: string, callback: FileWatcherCallback) {
                     const callbacks = fileWatcherCallbacks[filePath];
                     if (callbacks) {
-                        unorderedRemoveItem(callback, callbacks);
+                        unorderedRemoveItem(callbacks, callback);
                         if (callbacks.length === 0) {
                             delete fileWatcherCallbacks[filePath];
                         }
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index a0a647d4fd..6192e5db05 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -489,7 +489,7 @@ namespace ts {
             sourceFile.fileWatcher.close();
             sourceFile.fileWatcher = undefined;
             if (removed) {
-                unorderedRemoveItem(sourceFile.fileName, rootFileNames);
+                unorderedRemoveItem(rootFileNames, sourceFile.fileName);
             }
             startTimerForRecompilation();
         }
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index fc734a0cce..a07547d23b 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -1772,7 +1772,7 @@ namespace Harness {
                     tsConfig.options.configFilePath = data.name;
 
                     // delete entry from the list
-                    ts.removeItemAtPreservingOrder(testUnitData, i);
+                    ts.orderedRemoveItemAt(testUnitData, i);
 
                     break;
                 }
diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index f839aaabc1..6814305e6c 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -205,7 +205,7 @@ namespace ts {
                 referenceCount: 0,
                 directoryName,
                 close: () => {
-                    unorderedRemoveItem(cbWithRecursive, callbacks);
+                    unorderedRemoveItem(callbacks, cbWithRecursive);
                     if (!callbacks.length) {
                         delete this.watchedDirectories[path];
                     }
@@ -239,7 +239,7 @@ namespace ts {
             callbacks.push(callback);
             return {
                 close: () => {
-                    unorderedRemoveItem(callback, callbacks);
+                    unorderedRemoveItem(callbacks, callback);
                     if (!callbacks.length) {
                         delete this.watchedFiles[path];
                     }
@@ -254,7 +254,7 @@ namespace ts {
         };
         readonly clearTimeout = (timeoutId: any): void => {
             if (typeof timeoutId === "number") {
-                unorderedRemoveItemAt(this.callbackQueue, timeoutId);
+                orderedRemoveItemAt(this.callbackQueue, timeoutId);
             }
         };
 
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index ea66345cec..8381f16fa8 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -275,7 +275,7 @@ namespace ts.server {
         removeRoot(info: ScriptInfo) {
             if (this.filenameToScript.contains(info.path)) {
                 this.filenameToScript.remove(info.path);
-                unorderedRemoveItem(info, this.roots);
+                unorderedRemoveItem(this.roots, info);
                 this.resolvedModuleNames.remove(info.path);
                 this.resolvedTypeReferenceDirectives.remove(info.path);
             }
@@ -870,7 +870,7 @@ namespace ts.server {
                 project.directoryWatcher.close();
                 forEachProperty(project.directoriesWatchedForWildcards, watcher => { watcher.close(); });
                 delete project.directoriesWatchedForWildcards;
-                unorderedRemoveItem(project, this.configuredProjects);
+                unorderedRemoveItem(this.configuredProjects, project);
             }
             else {
                 for (const directory of project.directoriesWatchedForTsconfig) {
@@ -882,7 +882,7 @@ namespace ts.server {
                         delete project.projectService.directoryWatchersForTsconfig[directory];
                     }
                 }
-                unorderedRemoveItem(project, this.inferredProjects);
+                unorderedRemoveItem(this.inferredProjects, project);
             }
 
             const fileNames = project.getFileNames();
@@ -1007,7 +1007,7 @@ namespace ts.server {
                 }
             }
             else {
-                unorderedRemoveItem(info, this.openFilesReferenced);
+                unorderedRemoveItem(this.openFilesReferenced, info);
             }
             info.close();
         }
@@ -1514,13 +1514,13 @@ namespace ts.server {
                             // openFileRoots or openFileReferenced.
                             if (info.isOpen) {
                                 if (this.openFileRoots.indexOf(info) >= 0) {
-                                    unorderedRemoveItem(info, this.openFileRoots);
+                                    unorderedRemoveItem(this.openFileRoots, info);
                                     if (info.defaultProject && !info.defaultProject.isConfiguredProject()) {
                                         this.removeProject(info.defaultProject);
                                     }
                                 }
                                 if (this.openFilesReferenced.indexOf(info) >= 0) {
-                                    unorderedRemoveItem(info, this.openFilesReferenced);
+                                    unorderedRemoveItem(this.openFilesReferenced, info);
                                 }
                                 this.openFileRootsConfigured.push(info);
                                 info.defaultProject = project;
diff --git a/src/server/server.ts b/src/server/server.ts
index 04936e6721..2ce817fafa 100644
--- a/src/server/server.ts
+++ b/src/server/server.ts
@@ -267,7 +267,7 @@ namespace ts.server {
         }
 
         function removeFile(file: WatchedFile) {
-            unorderedRemoveItem(file, watchedFiles);
+            unorderedRemoveItem(watchedFiles, file);
         }
 
         return {