diff --git a/components/style/gecko/boxed_types.rs b/components/style/gecko/boxed_types.rs
new file mode 100644
index 00000000000..857f99e1489
--- /dev/null
+++ b/components/style/gecko/boxed_types.rs
@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! FFI implementations for types listed in ServoBoxedTypeList.h.
+
+use crate::gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
+use to_shmem::SharedMemoryBuilder;
+
+// TODO(heycam): The FFI impls for most of the types in ServoBoxedTypeList.h are spread across
+// various files at the moment, but should probably all move here, and use macros to define
+// them more succinctly, like we do in arc_types.rs.
+
+#[cfg(feature = "gecko")]
+unsafe impl HasFFI for SharedMemoryBuilder {
+    type FFIType = crate::gecko_bindings::bindings::RawServoSharedMemoryBuilder;
+}
+#[cfg(feature = "gecko")]
+unsafe impl HasSimpleFFI for SharedMemoryBuilder {}
+#[cfg(feature = "gecko")]
+unsafe impl HasBoxFFI for SharedMemoryBuilder {}
diff --git a/components/style/gecko/mod.rs b/components/style/gecko/mod.rs
index 1051f84fc52..fb332dcce6e 100644
--- a/components/style/gecko/mod.rs
+++ b/components/style/gecko/mod.rs
@@ -8,6 +8,7 @@
 mod non_ts_pseudo_class_list;
 
 pub mod arc_types;
+pub mod boxed_types;
 pub mod conversions;
 pub mod data;
 pub mod media_features;