diff --git a/tests/cases/unittests/cachingInServerLSHost.ts b/tests/cases/unittests/cachingInServerLSHost.ts
index 59f97f434e6..6d7b3fdbc28 100644
--- a/tests/cases/unittests/cachingInServerLSHost.ts
+++ b/tests/cases/unittests/cachingInServerLSHost.ts
@@ -123,7 +123,7 @@ module ts {
                     }
                     fileExistsIsCalled = true;
                     assert.isTrue(fileName.indexOf('/f2.') !== -1);
-                    return originalFileExists(fileName);
+                    return originalFileExists.call(serverHost, fileName);
                 };
                 let newContent = `import {x} from "f2"`;
                 rootScriptInfo.editContent(0, rootScriptInfo.content.length, newContent);
@@ -147,7 +147,7 @@ module ts {
                     }                    
                     fileExistsCalled = true;
                     assert.isTrue(fileName.indexOf('/f1.') !== -1);
-                    return originalFileExists(fileName);
+                    return originalFileExists.call(serverHost, fileName);
                 };
                 
                 let newContent = `import {x} from "f1"`;
@@ -192,7 +192,7 @@ module ts {
                     fileExistsCalledForBar = fileName.indexOf("/bar.") !== -1;
                 }
                 
-                return originalFileExists(fileName);
+                return originalFileExists.call(serverHost, fileName);
             };
             
             let { project, rootScriptInfo } = createProject(root.name, serverHost);