diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 44eae36d65470..eeebb1ef260f5 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2049,7 +2049,11 @@ namespace ts {
                 const file = filesByName.get(path);
                 // try to check if we've already seen this file but with a different casing in path
                 // NOTE: this only makes sense for case-insensitive file systems, and only on files which are not redirected
-                if (file && options.forceConsistentCasingInFileNames) {
+
+                // default to true
+                const forceCasing = options.forceConsistentCasingInFileNames || options.forceConsistentCasingInFileNames === undefined;
+
+                if (file && forceCasing) {
                     let inputName = fileName;
                     const checkedName = file.fileName;
                     const isRedirect = toPath(checkedName) !== toPath(inputName);
diff --git a/src/testRunner/unittests/moduleResolution.ts b/src/testRunner/unittests/moduleResolution.ts
index a3ebf4f84a7e2..38e2d7df2a77c 100644
--- a/src/testRunner/unittests/moduleResolution.ts
+++ b/src/testRunner/unittests/moduleResolution.ts
@@ -588,7 +588,7 @@ export = C;
                 "/a/b/c.ts": `/// <reference path="D.ts"/>`,
                 "/a/b/d.ts": "var x"
             });
-            test(files, { module: ModuleKind.AMD, forceConsistentCasingInFileNames: true }, "/a/b", /*useCaseSensitiveFileNames*/ false, ["c.ts", "d.ts"], [1149]);
+            test(files, { module: ModuleKind.AMD }, "/a/b", /*useCaseSensitiveFileNames*/ false, ["c.ts", "d.ts"], [1149]);
         });
 
         it("should fail when two files used in program differ only in casing (imports)", () => {
@@ -596,7 +596,7 @@ export = C;
                 "/a/b/c.ts": `import {x} from "D"`,
                 "/a/b/d.ts": "export var x"
             });
-            test(files, { module: ModuleKind.AMD, forceConsistentCasingInFileNames: true }, "/a/b", /*useCaseSensitiveFileNames*/ false, ["c.ts", "d.ts"], [1149]);
+            test(files, { module: ModuleKind.AMD }, "/a/b", /*useCaseSensitiveFileNames*/ false, ["c.ts", "d.ts"], [1149]);
         });
 
         it("should fail when two files used in program differ only in casing (imports, relative module names)", () => {
@@ -604,7 +604,7 @@ export = C;
                 "moduleA.ts": `import {x} from "./ModuleB"`,
                 "moduleB.ts": "export var x"
             });
-            test(files, { module: ModuleKind.CommonJS, forceConsistentCasingInFileNames: true }, "", /*useCaseSensitiveFileNames*/ false, ["moduleA.ts", "moduleB.ts"], [1149]);
+            test(files, { module: ModuleKind.CommonJS }, "", /*useCaseSensitiveFileNames*/ false, ["moduleA.ts", "moduleB.ts"], [1149]);
         });
 
         it("should fail when two files exist on disk that differs only in casing", () => {
@@ -622,7 +622,7 @@ export = C;
                 "moduleB.ts": `import a = require("./moduleC")`,
                 "moduleC.ts": "export var x"
             });
-            test(files, { module: ModuleKind.CommonJS, forceConsistentCasingInFileNames: true }, "", /*useCaseSensitiveFileNames*/ false, ["moduleA.ts", "moduleB.ts", "moduleC.ts"], [1149, 1149]);
+            test(files, { module: ModuleKind.CommonJS }, "", /*useCaseSensitiveFileNames*/ false, ["moduleA.ts", "moduleB.ts", "moduleC.ts"], [1149, 1149]);
         });
 
         it("should fail when module names in 'require' calls has inconsistent casing and current directory has uppercase chars", () => {
@@ -635,7 +635,7 @@ import a = require("./moduleA");
 import b = require("./moduleB");
                 `
             });
-            test(files, { module: ModuleKind.CommonJS, forceConsistentCasingInFileNames: true }, "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], [1149]);
+            test(files, { module: ModuleKind.CommonJS }, "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], [1149]);
         });
         it("should not fail when module names in 'require' calls has consistent casing and current directory has uppercase chars", () => {
             const files = createMapFromTemplate({
@@ -647,7 +647,7 @@ import a = require("./moduleA");
 import b = require("./moduleB");
                 `
             });
-            test(files, { module: ModuleKind.CommonJS, forceConsistentCasingInFileNames: true }, "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], []);
+            test(files, { module: ModuleKind.CommonJS }, "/a/B/c", /*useCaseSensitiveFileNames*/ false, ["moduleD.ts"], []);
         });
     });