diff --git a/src/mantle/http-client/class-pending-request.php b/src/mantle/http-client/class-pending-request.php
index b75155846..4251c7b00 100644
--- a/src/mantle/http-client/class-pending-request.php
+++ b/src/mantle/http-client/class-pending-request.php
@@ -228,7 +228,7 @@ public function body_format( string $format ) {
 	 * @return static
 	 */
 	public function content_type( string $content_type ) {
-		return $this->with_headers( [ 'Content-Type' => $content_type ] );
+		return $this->with_header( 'Content-Type', $content_type, true );
 	}
 
 	/**
diff --git a/tests/http-client/test-http-client.php b/tests/http-client/test-http-client.php
index 2a6280ca0..094079e4c 100644
--- a/tests/http-client/test-http-client.php
+++ b/tests/http-client/test-http-client.php
@@ -439,4 +439,11 @@ public function test_conditionable_unless_request() {
 
 		$this->assertEquals( 'Bar', $request->header( 'X-Foo' ) );
 	}
+
+	public function test_headers_as_form() {
+		$request = $this->http_factory
+			->as_form();
+
+		$this->assertEquals( 'application/x-www-form-urlencoded', $request->header( 'Content-Type' ) );
+	}
 }