diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 4dd6d8f6170b6..c92d147f9a93a 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1116,7 +1116,7 @@ namespace ts {
                     if (option && typeof option.type !== "string") {
                         const customOption = <CommandLineOptionOfCustomType>option;
                         // Validate custom option type
-                        if (!customOption.type.has(text)) {
+                        if (!customOption.type.has(text.toLowerCase())) {
                             errors.push(
                                 createDiagnosticForInvalidCustomType(
                                     customOption,
@@ -1811,7 +1811,7 @@ namespace ts {
             return value;
         }
         else if (typeof option.type !== "string") {
-            return option.type.get(value);
+            return option.type.get(typeof value === "string" ? value.toLowerCase() : value);
         }
         return normalizeNonListOptionValue(option, basePath, value);
     }
diff --git a/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.js b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.js
new file mode 100644
index 0000000000000..be1f2323a13b6
--- /dev/null
+++ b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.js
@@ -0,0 +1,25 @@
+//// [tests/cases/compiler/tsconfigMapOptionsAreCaseInsensitive.ts] ////
+
+//// [other.ts]
+export default 42;
+
+//// [index.ts]
+import Answer from "./other.js";
+const x = 10 + Answer;
+export {
+    x
+};
+
+//// [other.js]
+define(["require", "exports"], function (require, exports) {
+    "use strict";
+    exports.__esModule = true;
+    exports["default"] = 42;
+});
+//// [index.js]
+define(["require", "exports", "./other.js"], function (require, exports, other_js_1) {
+    "use strict";
+    exports.__esModule = true;
+    var x = 10 + other_js_1["default"];
+    exports.x = x;
+});
diff --git a/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.symbols b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.symbols
new file mode 100644
index 0000000000000..73a5bad9e56d4
--- /dev/null
+++ b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/other.ts ===
+export default 42;
+No type information for this code.
+No type information for this code.=== tests/cases/compiler/index.ts ===
+import Answer from "./other.js";
+>Answer : Symbol(Answer, Decl(index.ts, 0, 6))
+
+const x = 10 + Answer;
+>x : Symbol(x, Decl(index.ts, 1, 5))
+>Answer : Symbol(Answer, Decl(index.ts, 0, 6))
+
+export {
+    x
+>x : Symbol(x, Decl(index.ts, 2, 8))
+
+};
diff --git a/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.types b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.types
new file mode 100644
index 0000000000000..d82a1e42e95a8
--- /dev/null
+++ b/tests/baselines/reference/tsconfigMapOptionsAreCaseInsensitive.types
@@ -0,0 +1,18 @@
+=== tests/cases/compiler/other.ts ===
+export default 42;
+No type information for this code.
+No type information for this code.=== tests/cases/compiler/index.ts ===
+import Answer from "./other.js";
+>Answer : 42
+
+const x = 10 + Answer;
+>x : number
+>10 + Answer : number
+>10 : 10
+>Answer : 42
+
+export {
+    x
+>x : number
+
+};
diff --git a/tests/cases/compiler/tsconfigMapOptionsAreCaseInsensitive.ts b/tests/cases/compiler/tsconfigMapOptionsAreCaseInsensitive.ts
new file mode 100644
index 0000000000000..d825d6e7425e8
--- /dev/null
+++ b/tests/cases/compiler/tsconfigMapOptionsAreCaseInsensitive.ts
@@ -0,0 +1,16 @@
+// @filename: tsconfig.json
+{
+    "compilerOptions": {
+        "module": "AmD"
+    }
+}
+
+// @filename: other.ts
+export default 42;
+
+// @filename: index.ts
+import Answer from "./other.js";
+const x = 10 + Answer;
+export {
+    x
+};
\ No newline at end of file