diff --git a/BinaryMatrixEngine/ActionSet.cs b/BinaryMatrixEngine/ActionSet.cs
index 72a20ef..7e87b13 100644
--- a/BinaryMatrixEngine/ActionSet.cs
+++ b/BinaryMatrixEngine/ActionSet.cs
@@ -13,7 +13,7 @@ public interface CardSpecification {
 	public int? ResolveForPlayer(Player player);
 }
 
-public struct ActionSet {
+public readonly struct ActionSet {
 	public readonly ActionType type;
 	public readonly int lane;
 	public readonly CardSpecification? card;
@@ -34,7 +34,7 @@ public ActionSet(ActionType type, int lane) {
 		if(type != ActionType.DRAW && type != ActionType.COMBAT)
 			throw new ArgumentException("Invalid overload called for this type.", nameof(type));
 		this.type = type;
-		this.lane = lane;
+		this.lane = ValidateLane(lane, allowPseudo: type == ActionType.DRAW);
 		this.card = default;
 	}
 
@@ -42,7 +42,15 @@ public ActionSet(ActionType type, CardSpecification card, int lane) {
 		if(type != ActionType.PLAY && type != ActionType.FACEUP_PLAY && type != ActionType.DISCARD)
 			throw new ArgumentException("Invalid overload called for this type.", nameof(type));
 		this.type = type;
-		this.lane = lane;
+		this.lane = ValidateLane(lane, allowPseudo: type == ActionType.DISCARD);
 		this.card = card;
 	}
+
+	private static int ValidateLane(int lane, bool allowPseudo = false) {
+		return lane switch {
+			< 0 or > LANE_A => throw new ArgumentOutOfRangeException(nameof(lane), lane, "Lane must be within the range [0; " + LANE_A + "]."),
+			LANE_A when !allowPseudo => throw new ArgumentOutOfRangeException(nameof(lane), lane, "Lane must name a real lane, not the `a` pseudolane for this action."),
+			_ => lane
+		};
+	}
 }