diff --git a/src/utils/userAgent.ts b/src/utils/userAgent.ts
index 5da3107..69661b3 100644
--- a/src/utils/userAgent.ts
+++ b/src/utils/userAgent.ts
@@ -1,5 +1,70 @@
 import { UserAgent } from "../types";
 
+declare const Deno:
+  | {
+      version: {
+        deno: string;
+      };
+    }
+  | undefined;
+
+type EnvironmentDetectors = {
+  process?: {
+    versions?: {
+      node?: string;
+      bun?: string;
+    };
+  };
+  deno?: {
+    version?: {
+      deno?: string;
+    };
+  };
+  navigator?: {
+    userAgent?: string;
+  };
+};
+
+export const detectDefaultUserAgent = (
+  env: EnvironmentDetectors = {
+    process: typeof process !== "undefined" ? process : undefined,
+    deno: typeof Deno !== "undefined" ? Deno : undefined,
+    navigator: typeof navigator !== "undefined" ? navigator : undefined,
+  },
+): { userAgentString: string; defaultUserAgent: UserAgent } => {
+  let userAgentString = "";
+  if (env.navigator?.userAgent) {
+    userAgentString += env.navigator.userAgent;
+  }
+
+  const defaultAgent: UserAgent = {
+    sdk: { name: "JavaScript", version: "__SDK_VERSION__" },
+  };
+
+  if (env.deno?.version?.deno) {
+    defaultAgent.runtime_env = {
+      name: "Deno",
+      version: env.deno.version.deno,
+    };
+  } else if (env.process?.versions?.bun) {
+    defaultAgent.runtime_env = {
+      name: "Bun",
+      version: env.process.versions.bun,
+    };
+  } else if (env.process?.versions?.node) {
+    defaultAgent.runtime_env = {
+      name: "Node",
+      version: env.process.versions.node,
+    };
+  }
+
+  return { userAgentString, defaultUserAgent: defaultAgent };
+};
+
+const detected = detectDefaultUserAgent();
+const defaultUserAgentString = detected.userAgentString;
+const defaultUserAgent = detected.defaultUserAgent;
+
 export const buildUserAgent = (userAgent: UserAgent | false) =>
   defaultUserAgentString +
   (userAgent === false
@@ -11,41 +76,3 @@ export const buildUserAgent = (userAgent: UserAgent | false) =>
         )
         .join(" ") +
       ")");
-
-let defaultUserAgentString = "";
-if (typeof navigator !== "undefined" && navigator.userAgent) {
-  defaultUserAgentString += navigator.userAgent;
-}
-
-const defaultUserAgent: UserAgent = {
-  sdk: { name: "JavaScript", version: "__SDK_VERSION__" },
-};
-
-if (typeof process !== "undefined") {
-  if (process.versions.node && defaultUserAgentString.indexOf("Node") === -1) {
-    defaultUserAgent.runtime_env = {
-      name: "Node",
-      version: process.versions.node,
-    };
-  }
-  if (process.versions.bun && defaultUserAgentString.indexOf("Bun") === -1) {
-    defaultUserAgent.runtime_env = {
-      name: "Bun",
-      version: process.versions.bun,
-    };
-  }
-}
-
-declare const Deno:
-  | {
-      version: {
-        deno: string;
-      };
-    }
-  | undefined;
-
-if (typeof Deno !== "undefined") {
-  if (process.versions.bun && defaultUserAgentString.indexOf("Deno") === -1) {
-    defaultUserAgent.runtime_env = { name: "Deno", version: Deno.version.deno };
-  }
-}
diff --git a/tests/unit/utils.test.ts b/tests/unit/utils.test.ts
index 306bce2..f44e03c 100644
--- a/tests/unit/utils.test.ts
+++ b/tests/unit/utils.test.ts
@@ -1,7 +1,10 @@
 import fetchMock from "jest-fetch-mock";
 import { AssemblyAI } from "../../src";
 import { getPath } from "../../src/utils/path";
-import { buildUserAgent } from "../../src/utils/userAgent";
+import {
+  buildUserAgent,
+  detectDefaultUserAgent,
+} from "../../src/utils/userAgent";
 
 fetchMock.enableMocks();
 
@@ -120,4 +123,34 @@ describe("utils", () => {
     });
     await service.files.upload(new Blob());
   });
+
+  it("should detect Deno runtime environment", () => {
+    const { defaultUserAgent } = detectDefaultUserAgent({
+      deno: { version: { deno: "1.40.0" } },
+    });
+    expect(defaultUserAgent.runtime_env).toEqual({
+      name: "Deno",
+      version: "1.40.0",
+    });
+  });
+
+  it("should detect Bun runtime environment", () => {
+    const { defaultUserAgent } = detectDefaultUserAgent({
+      process: { versions: { bun: "1.1.0" } },
+    });
+    expect(defaultUserAgent.runtime_env).toEqual({
+      name: "Bun",
+      version: "1.1.0",
+    });
+  });
+
+  it("should detect Node runtime environment", () => {
+    const { defaultUserAgent } = detectDefaultUserAgent({
+      process: { versions: { node: "20.10.0" } },
+    });
+    expect(defaultUserAgent.runtime_env).toEqual({
+      name: "Node",
+      version: "20.10.0",
+    });
+  });
 });