diff --git a/test/node/rewriteRelativeImportExtension.test.js b/test/node/rewriteRelativeImportExtension.test.js
index 772d173..25158e1 100644
--- a/test/node/rewriteRelativeImportExtension.test.js
+++ b/test/node/rewriteRelativeImportExtension.test.js
@@ -7,6 +7,8 @@ testHelper("__rewriteRelativeImportExtension", __rewriteRelativeImportExtension
     assert.equal(__rewriteRelativeImportExtension("./foo.ts"), "./foo.js");
     assert.equal(__rewriteRelativeImportExtension("../foo.ts"), "../foo.js");
     assert.equal(__rewriteRelativeImportExtension("../../foo.ts"), "../../foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.TS"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.Ts"), "./foo.js");
   });
 
   test("rewrites other TypeScript extensions", () => {
@@ -14,6 +16,7 @@ testHelper("__rewriteRelativeImportExtension", __rewriteRelativeImportExtension
     assert.equal(__rewriteRelativeImportExtension("./foo.cts"), "./foo.cjs");
     assert.equal(__rewriteRelativeImportExtension("./foo.tsx"), "./foo.js");
     assert.equal(__rewriteRelativeImportExtension("./foo.tsx", true), "./foo.jsx");
+    assert.equal(__rewriteRelativeImportExtension("./foo.Tsx", true), "./foo.jsx");
   });
 
   test("does not rewrite other extensions", () => {
@@ -45,5 +48,6 @@ testHelper("__rewriteRelativeImportExtension", __rewriteRelativeImportExtension
     assert.equal(__rewriteRelativeImportExtension("./foo.d.mts"), "./foo.d.mts");
     assert.equal(__rewriteRelativeImportExtension("./foo.d.cts"), "./foo.d.cts");
     assert.equal(__rewriteRelativeImportExtension("./foo.d.css.ts"), "./foo.d.css.ts");
+    assert.equal(__rewriteRelativeImportExtension("./foo.D.ts"), "./foo.D.ts");
   });
 });
diff --git a/tslib.es6.js b/tslib.es6.js
index a1323a6..36b58a5 100644
--- a/tslib.es6.js
+++ b/tslib.es6.js
@@ -350,17 +350,18 @@ export function __disposeResources(env) {
 
 export function __rewriteRelativeImportExtension(path, preserveJsx) {
     if (typeof path === "string" && path[0] === "." && (path[1] === "/" || path[1] === "." && path[2] === "/")) {
-        if (path.substring(path.length - 4) === ".tsx") {
+        if (path.substring(path.length - 4).toLowerCase() === ".tsx") {
             return path.substring(0, path.length - 4) + (preserveJsx ? ".jsx" : ".js");
         }
-        if (path.substring(path.length - 3) === ".ts") {
-            var dot = path.lastIndexOf(".", path.length - 4);
-            if (dot >= 0 && (path.substring(dot - 2, dot) === ".d" || path.substring(dot, dot + 2) === ".d")) {
+        var extMatch = path.match(/\.[cm]?ts$/i);
+        if (extMatch) {
+            var ext = extMatch[0].toLowerCase();
+            var dot = path.lastIndexOf(".", path.length - (ext.length + 1));
+            if (dot >= 0 && (path.substring(dot - 2, dot).toLowerCase() === ".d" || path.substring(dot, dot + 2).toLowerCase() === ".d")) {
                 return path;
             }
-            return path.substring(0, path.length - 3) + ".js";
+            return path.substring(0, path.length - ext.length) + (ext === ".mts" ? ".mjs" : ext === ".cts" ? ".cjs" : ".js");
         }
-        return path.replace(/(?<!\.d)\.[cm]ts$/, function (ext) { return ext === ".mts" ? ".mjs" : ".cjs"; });
     }
     return path;
 }
diff --git a/tslib.es6.mjs b/tslib.es6.mjs
index e225e43..ccffef3 100644
--- a/tslib.es6.mjs
+++ b/tslib.es6.mjs
@@ -349,17 +349,18 @@ export function __disposeResources(env) {
 
 export function __rewriteRelativeImportExtension(path, preserveJsx) {
   if (typeof path === "string" && path[0] === "." && (path[1] === "/" || path[1] === "." && path[2] === "/")) {
-    if (path.substring(path.length - 4) === ".tsx") {
-      return path.substring(0, path.length - 4) + (preserveJsx ? ".jsx" : ".js");
-    }
-    if (path.substring(path.length - 3) === ".ts") {
-      var dot = path.lastIndexOf(".", path.length - 4);
-      if (dot >= 0 && (path.substring(dot - 2, dot) === ".d" || path.substring(dot, dot + 2) === ".d")) {
-        return path;
+      if (path.substring(path.length - 4).toLowerCase() === ".tsx") {
+          return path.substring(0, path.length - 4) + (preserveJsx ? ".jsx" : ".js");
+      }
+      var extMatch = path.match(/\.[cm]?ts$/i);
+      if (extMatch) {
+          var ext = extMatch[0].toLowerCase();
+          var dot = path.lastIndexOf(".", path.length - (ext.length + 1));
+          if (dot >= 0 && (path.substring(dot - 2, dot).toLowerCase() === ".d" || path.substring(dot, dot + 2).toLowerCase() === ".d")) {
+              return path;
+          }
+          return path.substring(0, path.length - ext.length) + (ext === ".mts" ? ".mjs" : ext === ".cts" ? ".cjs" : ".js");
       }
-      return path.substring(0, path.length - 3) + ".js";
-    }
-    return path.replace(/(?<!\.d)\.[cm]ts$/, function (ext) { return ext === ".mts" ? ".mjs" : ".cjs"; });
   }
   return path;
 }
diff --git a/tslib.js b/tslib.js
index 6587aa1..64090f0 100644
--- a/tslib.js
+++ b/tslib.js
@@ -398,17 +398,18 @@ var __rewriteRelativeImportExtension;
 
     __rewriteRelativeImportExtension = function (path, preserveJsx) {
         if (typeof path === "string" && path[0] === "." && (path[1] === "/" || path[1] === "." && path[2] === "/")) {
-            if (path.substring(path.length - 4) === ".tsx") {
+            if (path.substring(path.length - 4).toLowerCase() === ".tsx") {
                 return path.substring(0, path.length - 4) + (preserveJsx ? ".jsx" : ".js");
             }
-            if (path.substring(path.length - 3) === ".ts") {
-                var dot = path.lastIndexOf(".", path.length - 4);
-                if (dot >= 0 && (path.substring(dot - 2, dot) === ".d" || path.substring(dot, dot + 2) === ".d")) {
+            var extMatch = path.match(/\.[cm]?ts$/i);
+            if (extMatch) {
+                var ext = extMatch[0].toLowerCase();
+                var dot = path.lastIndexOf(".", path.length - (ext.length + 1));
+                if (dot >= 0 && (path.substring(dot - 2, dot).toLowerCase() === ".d" || path.substring(dot, dot + 2).toLowerCase() === ".d")) {
                     return path;
                 }
-                return path.substring(0, path.length - 3) + ".js";
+                return path.substring(0, path.length - ext.length) + (ext === ".mts" ? ".mjs" : ext === ".cts" ? ".cjs" : ".js");
             }
-            return path.replace(/(?<!\.d)\.[cm]ts$/, function (ext) { return ext === ".mts" ? ".mjs" : ".cjs"; });
         }
         return path;
     };