diff --git a/OpenRA.Mods.Cnc/Traits/MadTank.cs b/OpenRA.Mods.Cnc/Traits/MadTank.cs
index 8bd499a622..3289221824 100644
--- a/OpenRA.Mods.Cnc/Traits/MadTank.cs
+++ b/OpenRA.Mods.Cnc/Traits/MadTank.cs
@@ -56,8 +56,19 @@ namespace OpenRA.Mods.Cnc.Traits
 		public object Create(ActorInitializer init) { return new MadTank(init.Self, this); }
 		public void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			ThumpDamageWeaponInfo = rules.Weapons[ThumpDamageWeapon.ToLowerInvariant()];
-			DetonationWeaponInfo = rules.Weapons[DetonationWeapon.ToLowerInvariant()];
+			WeaponInfo thumpDamageWeapon;
+			WeaponInfo detonationWeapon;
+			var thumpDamageWeaponToLower = (ThumpDamageWeapon ?? string.Empty).ToLowerInvariant();
+			var detonationWeaponToLower = (DetonationWeapon ?? string.Empty).ToLowerInvariant();
+
+			if (!rules.Weapons.TryGetValue(thumpDamageWeaponToLower, out thumpDamageWeapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(thumpDamageWeaponToLower));
+
+			if (!rules.Weapons.TryGetValue(detonationWeaponToLower, out detonationWeapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(detonationWeaponToLower));
+
+			ThumpDamageWeaponInfo = thumpDamageWeapon;
+			DetonationWeaponInfo = detonationWeapon;
 		}
 	}
 
diff --git a/OpenRA.Mods.Cnc/Traits/SupportPowers/IonCannonPower.cs b/OpenRA.Mods.Cnc/Traits/SupportPowers/IonCannonPower.cs
index b2eaba51bf..526ad72d55 100644
--- a/OpenRA.Mods.Cnc/Traits/SupportPowers/IonCannonPower.cs
+++ b/OpenRA.Mods.Cnc/Traits/SupportPowers/IonCannonPower.cs
@@ -49,7 +49,13 @@ namespace OpenRA.Mods.Cnc.Traits
 		public override object Create(ActorInitializer init) { return new IonCannonPower(init.Self, this); }
 		public override void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			WeaponInfo = rules.Weapons[Weapon.ToLowerInvariant()];
+			WeaponInfo weapon;
+			var weaponToLower = (Weapon ?? string.Empty).ToLowerInvariant();
+			if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+
+			WeaponInfo = weapon;
+
 			base.RulesetLoaded(rules, ai);
 		}
 	}
diff --git a/OpenRA.Mods.Common/Traits/Air/FallsToEarth.cs b/OpenRA.Mods.Common/Traits/Air/FallsToEarth.cs
index 1670e55e61..4ebf09ab94 100644
--- a/OpenRA.Mods.Common/Traits/Air/FallsToEarth.cs
+++ b/OpenRA.Mods.Common/Traits/Air/FallsToEarth.cs
@@ -30,7 +30,15 @@ namespace OpenRA.Mods.Common.Traits
 		public object Create(ActorInitializer init) { return new FallsToEarth(init.Self, this); }
 		public void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			ExplosionWeapon = string.IsNullOrEmpty(Explosion) ? null : rules.Weapons[Explosion.ToLowerInvariant()];
+			if (string.IsNullOrEmpty(Explosion))
+				return;
+
+			WeaponInfo weapon;
+			var weaponToLower = Explosion.ToLowerInvariant();
+			if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+
+			ExplosionWeapon = weapon;
 		}
 	}
 
diff --git a/OpenRA.Mods.Common/Traits/Buildings/GroundLevelBridge.cs b/OpenRA.Mods.Common/Traits/Buildings/GroundLevelBridge.cs
index b91643b381..2e0b601126 100644
--- a/OpenRA.Mods.Common/Traits/Buildings/GroundLevelBridge.cs
+++ b/OpenRA.Mods.Common/Traits/Buildings/GroundLevelBridge.cs
@@ -30,7 +30,15 @@ namespace OpenRA.Mods.Common.Traits
 
 		public WeaponInfo DemolishWeaponInfo { get; private set; }
 
-		public void RulesetLoaded(Ruleset rules, ActorInfo ai) { DemolishWeaponInfo = rules.Weapons[DemolishWeapon.ToLowerInvariant()]; }
+		public void RulesetLoaded(Ruleset rules, ActorInfo ai)
+		{
+			WeaponInfo weapon;
+			var weaponToLower = (DemolishWeapon ?? string.Empty).ToLowerInvariant();
+			if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+
+			DemolishWeaponInfo = weapon;
+		}
 
 		public object Create(ActorInitializer init) { return new GroundLevelBridge(init.Self, this); }
 	}
diff --git a/OpenRA.Mods.Common/Traits/Explodes.cs b/OpenRA.Mods.Common/Traits/Explodes.cs
index a8ab0695f0..13647337c2 100644
--- a/OpenRA.Mods.Common/Traits/Explodes.cs
+++ b/OpenRA.Mods.Common/Traits/Explodes.cs
@@ -50,8 +50,23 @@ namespace OpenRA.Mods.Common.Traits
 		public override object Create(ActorInitializer init) { return new Explodes(this, init.Self); }
 		public override void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			WeaponInfo = string.IsNullOrEmpty(Weapon) ? null : rules.Weapons[Weapon.ToLowerInvariant()];
-			EmptyWeaponInfo = string.IsNullOrEmpty(EmptyWeapon) ? null : rules.Weapons[EmptyWeapon.ToLowerInvariant()];
+			if (!string.IsNullOrEmpty(Weapon))
+			{
+				WeaponInfo weapon;
+				var weaponToLower = Weapon.ToLowerInvariant();
+				if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+					throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+				WeaponInfo = weapon;
+			}
+
+			if (!string.IsNullOrEmpty(EmptyWeapon))
+			{
+				WeaponInfo emptyWeapon;
+				var emptyWeaponToLower = EmptyWeapon.ToLowerInvariant();
+				if (!rules.Weapons.TryGetValue(emptyWeaponToLower, out emptyWeapon))
+					throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(emptyWeaponToLower));
+				EmptyWeaponInfo = emptyWeapon;
+			}
 
 			base.RulesetLoaded(rules, ai);
 		}
diff --git a/OpenRA.Mods.Common/Traits/ExplosionOnDamageTransition.cs b/OpenRA.Mods.Common/Traits/ExplosionOnDamageTransition.cs
index 896751b0e4..b32f974a86 100644
--- a/OpenRA.Mods.Common/Traits/ExplosionOnDamageTransition.cs
+++ b/OpenRA.Mods.Common/Traits/ExplosionOnDamageTransition.cs
@@ -35,7 +35,15 @@ namespace OpenRA.Mods.Common.Traits
 
 		public void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			WeaponInfo = string.IsNullOrEmpty(Weapon) ? null : rules.Weapons[Weapon.ToLowerInvariant()];
+			if (string.IsNullOrEmpty(Weapon))
+				return;
+
+			WeaponInfo weapon;
+			var weaponToLower = Weapon.ToLowerInvariant();
+			if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+
+			WeaponInfo = weapon;
 		}
 	}
 
diff --git a/OpenRA.Mods.Common/Traits/SupportPowers/NukePower.cs b/OpenRA.Mods.Common/Traits/SupportPowers/NukePower.cs
index c408cb1cdd..a74f32f153 100644
--- a/OpenRA.Mods.Common/Traits/SupportPowers/NukePower.cs
+++ b/OpenRA.Mods.Common/Traits/SupportPowers/NukePower.cs
@@ -80,7 +80,13 @@ namespace OpenRA.Mods.Common.Traits
 		public override object Create(ActorInitializer init) { return new NukePower(init.Self, this); }
 		public override void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			WeaponInfo = rules.Weapons[MissileWeapon.ToLowerInvariant()];
+			WeaponInfo weapon;
+			var weaponToLower = (MissileWeapon ?? string.Empty).ToLowerInvariant();
+			if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+				throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+
+			WeaponInfo = weapon;
+
 			base.RulesetLoaded(rules, ai);
 		}
 	}
diff --git a/OpenRA.Mods.Common/Traits/ThrowsShrapnel.cs b/OpenRA.Mods.Common/Traits/ThrowsShrapnel.cs
index 1651f3d197..d8d73aa459 100644
--- a/OpenRA.Mods.Common/Traits/ThrowsShrapnel.cs
+++ b/OpenRA.Mods.Common/Traits/ThrowsShrapnel.cs
@@ -33,7 +33,14 @@ namespace OpenRA.Mods.Common.Traits
 		public object Create(ActorInitializer actor) { return new ThrowsShrapnel(this); }
 		public void RulesetLoaded(Ruleset rules, ActorInfo ai)
 		{
-			WeaponInfos = Weapons.Select(w => rules.Weapons[w.ToLowerInvariant()]).ToArray();
+			WeaponInfos = Weapons.Select(w =>
+			{
+				WeaponInfo weapon;
+				var weaponToLower = w.ToLowerInvariant();
+				if (!rules.Weapons.TryGetValue(weaponToLower, out weapon))
+					throw new YamlException("Weapons Ruleset does not contain an entry '{0}'".F(weaponToLower));
+				return weapon;
+			}).ToArray();
 		}
 	}