diff --git a/doc/ipc-design.md b/doc/ipc-design.md
index 2e011ec2c..68bf27f9c 100644
--- a/doc/ipc-design.md
+++ b/doc/ipc-design.md
@@ -228,3 +228,12 @@ for details.
 [SCM_RIGHTS]: https://man7.org/linux/man-pages/man3/cmsg.3.html
 [win32handles]: https://lackingrhoticity.blogspot.com/2015/05/passing-fds-handles-between-processes.html
 [WinSCM_RIGHTS]: https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/#unsupportedunavailable
+
+## 32 bits client support on 64 bits server
+
+On 64 bits system, the server process will typically be a 64 bits executable,
+clients may be 32 or 64 bits. As IPC either through socket or shared memory will
+share C struct directly, we must pay attention to memory layout.
+
+All data types must be fixed size and alignments must be based on the 64 bits
+targets. On Linux this mostly means `alignas(8)` must be used for (u)int64_t.
diff --git a/src/xrt/include/xrt/xrt_compositor.h b/src/xrt/include/xrt/xrt_compositor.h
index e9900507e..24d2f7ba8 100644
--- a/src/xrt/include/xrt/xrt_compositor.h
+++ b/src/xrt/include/xrt/xrt_compositor.h
@@ -409,6 +409,8 @@ struct xrt_layer_data
 	 *
 	 * The layer may be displayed after this point, but must never be
 	 * displayed before.
+	 *
+	 * alignas for 32 bit client support,
 	 */
 	alignas(8) int64_t timestamp;
 
@@ -478,6 +480,7 @@ struct xrt_layer_data
  */
 struct xrt_layer_frame_data
 {
+	//! alignas for 32 bit client support, see @ref ipc-design
 	alignas(8) int64_t frame_id;
 	int64_t display_time_ns;
 	enum xrt_blend_mode env_blend_mode;
@@ -931,6 +934,7 @@ struct xrt_swapchain_create_properties
 struct xrt_session_info
 {
 	bool is_overlay;
+	//! alignas for 32 bit client support, see @ref ipc-design
 	alignas(8) uint64_t flags;
 	uint32_t z_order;
 };
@@ -945,7 +949,10 @@ struct xrt_compositor_info
 	//! Number of formats, never changes.
 	uint32_t format_count;
 
-	//! Supported formats, never changes.
+	/*!
+	 * Supported formats, never changes.
+	 * alignas for 32 bit client support, see @ref ipc-design
+	 */
 	alignas(8) int64_t formats[XRT_MAX_SWAPCHAIN_FORMATS];
 
 	//! Max texture size that GPU supports (size of a single dimension), zero means any size.
diff --git a/src/xrt/include/xrt/xrt_device.h b/src/xrt/include/xrt/xrt_device.h
index c0450efa1..dd17b1724 100644
--- a/src/xrt/include/xrt/xrt_device.h
+++ b/src/xrt/include/xrt/xrt_device.h
@@ -164,6 +164,7 @@ struct xrt_input
 	//! Is this input active.
 	bool active;
 
+	//! alignas for 32 bit client support, see @ref ipc-design
 	alignas(8) int64_t timestamp;
 
 	enum xrt_input_name name;
diff --git a/src/xrt/include/xrt/xrt_system.h b/src/xrt/include/xrt/xrt_system.h
index 356fa462f..995f71bc3 100644
--- a/src/xrt/include/xrt/xrt_system.h
+++ b/src/xrt/include/xrt/xrt_system.h
@@ -169,6 +169,8 @@ struct xrt_system_roles
 	 * All valid values are greater then zero; this is to
 	 * make init easier where any cache can start at zero and be guaranteed
 	 * to be replaced with a new @ref xrt_system_roles.
+	 *
+	 * alignas for 32 bit client support, see @ref ipc-design
 	 */
 	alignas(8) uint64_t generation_id;