diff --git a/crates/composition/src/shell.rs b/crates/composition/src/shell.rs
index 3dd42f8..f3264dd 100644
--- a/crates/composition/src/shell.rs
+++ b/crates/composition/src/shell.rs
@@ -405,6 +405,10 @@ impl Shell {
             }));
         }
 
+        for def in &definitions {
+            def.config.validate().map_err(Error::Domain)?;
+        }
+
         let is_single_window = definitions.len() == 1;
 
         if is_single_window {
@@ -693,6 +697,12 @@ impl Shell {
         config: &SurfaceConfig,
     ) {
         log::debug!("Surface command: ApplyConfig {:?}", target);
+
+        if let Err(e) = config.validate() {
+            log::error!("Invalid surface configuration: {}", e);
+            return;
+        }
+
         for surface in Self::resolve_surface_target(ctx, target) {
             let handle = LayerSurfaceHandle::from_window_state(surface);
 
diff --git a/crates/domain/src/config.rs b/crates/domain/src/config.rs
index 3536330..6bcec07 100644
--- a/crates/domain/src/config.rs
+++ b/crates/domain/src/config.rs
@@ -1,4 +1,5 @@
 use crate::dimensions::ScaleFactor;
+use crate::errors::{DomainError, Result};
 use crate::value_objects::anchor::AnchorEdges;
 use crate::value_objects::dimensions::SurfaceDimension;
 use crate::value_objects::keyboard_interactivity::KeyboardInteractivity;
@@ -10,6 +11,14 @@ use crate::value_objects::output_policy::OutputPolicy;
 ///
 /// Contains all positioning, sizing, and behavioral properties for a surface.
 /// Use with `ShellConfig` for declarative configuration or build via `ShellBuilder`.
+///
+/// # Wayland Protocol Requirements
+///
+/// According to the wlr-layer-shell protocol, dimensions and anchors must be coordinated:
+/// - If width is 0, the surface must be anchored to both left and right edges
+/// - If height is 0, the surface must be anchored to both top and bottom edges
+///
+/// Use `validate()` to check protocol compliance before use.
 #[derive(Debug, Clone)]
 pub struct SurfaceConfig {
     pub dimensions: SurfaceDimension,
@@ -38,6 +47,33 @@ impl SurfaceConfig {
             output_policy: OutputPolicy::default(),
         }
     }
+
+    /// Validates the surface configuration according to Wayland layer-shell protocol requirements.
+    ///
+    /// According to the protocol:
+    /// - If width is 0, the surface must be anchored to both left and right edges
+    /// - If height is 0, the surface must be anchored to both top and bottom edges
+    pub fn validate(&self) -> Result<()> {
+        if self.dimensions.width() == 0 && !(self.anchor.has_left() && self.anchor.has_right()) {
+            return Err(DomainError::Configuration {
+                message: "Width is 0 but surface is not anchored to both left and right edges. \
+                          According to wlr-layer-shell protocol, you must set your anchor to \
+                          opposite edges in the dimensions you omit."
+                    .to_string(),
+            });
+        }
+
+        if self.dimensions.height() == 0 && !(self.anchor.has_top() && self.anchor.has_bottom()) {
+            return Err(DomainError::Configuration {
+                message: "Height is 0 but surface is not anchored to both top and bottom edges. \
+                          According to wlr-layer-shell protocol, you must set your anchor to \
+                          opposite edges in the dimensions you omit."
+                    .to_string(),
+            });
+        }
+
+        Ok(())
+    }
 }
 
 impl Default for SurfaceConfig {
diff --git a/crates/domain/src/value_objects/dimensions.rs b/crates/domain/src/value_objects/dimensions.rs
index a6d41c2..7e05a0c 100644
--- a/crates/domain/src/value_objects/dimensions.rs
+++ b/crates/domain/src/value_objects/dimensions.rs
@@ -1,26 +1,24 @@
 /// Width and height of a layer surface in pixels
 ///
-/// Use 0 for either dimension to let the surface stretch along that axis based on anchor edges.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// According to the Wayland wlr-layer-shell protocol:
+/// - Pass 0 for either width or height to have the compositor assign it
+/// - The compositor will center the surface with respect to its anchors
+/// - When using 0, you MUST anchor to opposite edges in that dimension:
+///   - width = 0 requires both left and right anchors
+///   - height = 0 requires both top and bottom anchors
+/// - Not following this requirement is a protocol error
+/// - Both values default to 0
+///
+/// Size is double-buffered via `wl_surface.commit`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
 pub struct SurfaceDimension {
     width: u32,
     height: u32,
 }
 
 impl SurfaceDimension {
-    pub fn new(width: u32, height: u32) -> Self {
-        Self {
-            width: if width == 0 {
-                Self::default().width
-            } else {
-                width
-            },
-            height: if height == 0 {
-                Self::default().height
-            } else {
-                height
-            },
-        }
+    pub const fn new(width: u32, height: u32) -> Self {
+        Self { width, height }
     }
 
     pub const fn from_raw(width: u32, height: u32) -> Self {
@@ -36,15 +34,6 @@ impl SurfaceDimension {
     }
 }
 
-impl Default for SurfaceDimension {
-    fn default() -> Self {
-        Self {
-            width: 20,
-            height: 20,
-        }
-    }
-}
-
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct PopupDimensions {
     pub width: f32,