diff --git a/scripts/build_npm.ts b/scripts/build_npm.ts
index e2852eb..a2eb72b 100644
--- a/scripts/build_npm.ts
+++ b/scripts/build_npm.ts
@@ -1,4 +1,4 @@
-import { build, emptyDir, copy } from "./deps.ts";
+import { build, copy, emptyDir } from "./deps.ts";
 
 // Clear NPM directory
 await emptyDir("./npm");
@@ -16,7 +16,7 @@ await build({
   mappings: {
     "https://deno.land/x/zipjs@v2.7.17/index.js": {
       name: "@zip.js/zip.js",
-      version: "^2.7.17"
+      version: "^2.7.17",
     },
   },
   package: {
@@ -26,14 +26,14 @@ await build({
     description: "ENTSO-e transparency platform API Client. Complete. Easy to use. Minimal.",
     license: "MIT",
     repository: {
-        type: "git",
-        url: "git+https://github.com/Hexagon/entsoe-api-client.git"
+      type: "git",
+      url: "git+https://github.com/Hexagon/entsoe-api-client.git",
     },
     author: "Hexagon <Hexagon@GitHub>",
     bugs: {
-        url: "https://github.com/Hexagon/entsoe-api-client/issues"
+      url: "https://github.com/Hexagon/entsoe-api-client/issues",
     },
-    homepage: "https://github.com/Hexagon/entsoe-api-client#readme"
+    homepage: "https://github.com/Hexagon/entsoe-api-client#readme",
   },
 });
 
@@ -41,11 +41,19 @@ await build({
 Deno.copyFileSync("LICENSE", "npm/LICENSE");
 Deno.copyFileSync("README.md", "npm/README.md");
 
-// npmignore test data
-// ensure the test data is ignored in the `.npmignore` file
-// so it doesn't get published with your npm package
+// Fix the .npmignore file to prevent exclusion of esm/src/ and script/src/
+// DNT 0.37.0 generates "src/" in .npmignore by default (when not using source maps).
+// This pattern inadvertently excludes esm/src/ and script/src/ containing transpiled code.
+// Replace "src/" with "/src/" to only match the root TypeScript source directory.
+let npmignore = await Deno.readTextFile("npm/.npmignore");
+npmignore = npmignore.replace(/^src\/$/m, "/src/");
+await Deno.writeTextFile("npm/.npmignore", npmignore);
+
+// npmignore test data and test declaration files
+// ensure the test data and generated test .d.ts files are ignored in the `.npmignore` file
+// so they don't get published with your npm package
 await Deno.writeTextFile(
   "npm/.npmignore",
-  "esm/tests/data\nscript/tests/data\n",
+  "esm/tests/data\nscript/tests/data\n*.test.d.ts\ntests/**/*.d.ts\n",
   { append: true },
-);
\ No newline at end of file
+);