diff --git a/src/container.zig b/src/container.zig
index 37591fc..e773fa5 100644
--- a/src/container.zig
+++ b/src/container.zig
@@ -727,14 +727,18 @@ pub fn Container(Model: type, Event: type) type {
             // assign currently calculated size
             this.size = switch (this.properties.size.grow) {
                 .both => .max(size, this.properties.size.dim),
-                .fixed => if (this.properties.size.dim.x > 0 and this.properties.size.dim.y > 0) this.properties.size.dim else size,
-                .horizontal => .{
-                    .x = @max(size.x, this.properties.size.dim.x),
-                    .y = if (this.properties.size.dim.y > 0) this.properties.size.dim.y else size.y,
+                .fixed => blk: {
+                    assert(this.properties.size.dim.x > 0 or size.x > 0);
+                    assert(this.properties.size.dim.y > 0 or size.y > 0);
+                    break :blk .max(size, this.properties.size.dim);
                 },
-                .vertical => .{
-                    .x = if (this.properties.size.dim.x > 0) this.properties.size.dim.x else size.x,
-                    .y = @max(size.y, this.properties.size.dim.y),
+                .horizontal => blk: {
+                    assert(this.properties.size.dim.y > 0 or size.y > 0);
+                    break :blk .max(size, this.properties.size.dim);
+                },
+                .vertical => blk: {
+                    assert(this.properties.size.dim.x > 0 or size.x > 0);
+                    break :blk .max(size, this.properties.size.dim);
                 },
             };
             return this.size;