diff --git a/.github/workflows/quicktest.yml b/.github/workflows/quicktest.yml
index b0bd62620..27dfdd8e2 100644
--- a/.github/workflows/quicktest.yml
+++ b/.github/workflows/quicktest.yml
@@ -79,6 +79,9 @@ jobs:
       - name: Access localhost on port 9002
         run: curl -i http://localhost:9002
 
+      - name: Show available locales
+        run: locale -a
+
       - name: Show PHPUnit version
         run: vendor/bin/phpunit --version
 
diff --git a/tests/Transport/FsockopenTest.php b/tests/Transport/FsockopenTest.php
index 5af8e7639..f9b1c987f 100644
--- a/tests/Transport/FsockopenTest.php
+++ b/tests/Transport/FsockopenTest.php
@@ -53,4 +53,33 @@ public function testContentLengthHeader() {
 	public function checkContentLengthHeader($headers) {
 		$this->assertStringContainsString('Content-Length: 0', $headers);
 	}
+
+	/**
+	 * Issue #335/#339.
+	 */
+	public function testHTTPVersionHeader() {
+		// Remember the original locale.
+		$locale = setlocale(LC_NUMERIC, 0);
+
+		// Set the locale to one using commas for the decimal point.
+		setlocale(LC_NUMERIC, 'de_DE@euro', 'de_DE', 'de', 'ge');
+
+		// Make sure the locale was changed.
+		$this->assertNotSame($locale, setlocale(LC_NUMERIC, 0), 'Changing the locale failed');
+
+		$hooks = new Requests_Hooks();
+		$hooks->register('fsockopen.after_headers', array($this, 'checkHTTPVersionHeader'));
+
+		Requests::post(httpbin('/post'), array(), array(), $this->getOptions(array('hooks' => $hooks)));
+
+		// Reset the locale.
+		setlocale(LC_NUMERIC, $locale);
+	}
+
+	/**
+	 * Issue #335/#339.
+	 */
+	public function checkHTTPVersionHeader($headers) {
+		$this->assertStringContainsString('HTTP/1.1', $headers, 'HTTP header is influenced by the system locale');
+	}
 }