diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index d2ea69b304d..808f8a538df 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1243,6 +1243,8 @@ namespace ts {
      *  List of supported extensions in order of file resolution precedence.
      */
     export const supportedTypeScriptExtensions = [".ts", ".tsx", ".d.ts"];
+    /** Must have ".d.ts" first because if ".ts" goes first, that will be detected as the extension instead of ".d.ts". */
+    export const supportedTypescriptExtensionsForExtractExtension = [".d.ts", ".ts", ".tsx"];
     export const supportedJavascriptExtensions = [".js", ".jsx"];
     const allSupportedExtensions  = supportedTypeScriptExtensions.concat(supportedJavascriptExtensions);
 
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 8b32d5351ea..faf210e461f 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -2713,12 +2713,10 @@ namespace ts {
         return forEach(supportedTypeScriptExtensions, extension => fileExtensionIs(fileName, extension));
     }
 
-    /** Return ".ts" or ".tsx" if that is the extension. */
+    /** Return ".ts", ".d.ts", or ".tsx", if that is the extension. */
     export function tryExtractTypeScriptExtension(fileName: string): string | undefined {
-        return find(supportedTypescriptExtensionsWithDtsFirst, extension => fileExtensionIs(fileName, extension));
+        return find(supportedTypescriptExtensionsForExtractExtension, extension => fileExtensionIs(fileName, extension));
     }
-    // Must have '.d.ts' first because if '.ts' goes first, that will be detected as the extension instead of '.d.ts'.
-    const supportedTypescriptExtensionsWithDtsFirst = supportedTypeScriptExtensions.slice().reverse();
 
     /**
      * Replace each instance of non-ascii characters by one, two, three, or four escape sequences