diff --git a/spine-lua/AnimationState.lua b/spine-lua/AnimationState.lua
index 289bb7fcd..af79a8bb6 100644
--- a/spine-lua/AnimationState.lua
+++ b/spine-lua/AnimationState.lua
@@ -168,7 +168,7 @@ function AnimationState.new (data)
 
 	function self:setAnimationByName (trackIndex, animationName, loop)
 		local animation = self.data.skeletonData:findAnimation(animationName)
-		if not animation then error("Animation not found: " + animationName) end
+		if not animation then error("Animation not found: " .. animationName) end
 		return self:setAnimation(trackIndex, animation, loop)
 	end
 
@@ -184,7 +184,7 @@ function AnimationState.new (data)
 
 	function self:addAnimationByName (trackIndex, animationName, loop, delay)
 		local animation = self.data.skeletonData:findAnimation(animationName)
-		if not animation then error("Animation not found: " + animationName) end
+		if not animation then error("Animation not found: " .. animationName) end
 		return self:addAnimation(trackIndex, animation, loop, delay)
 	end
 
diff --git a/spine-lua/Skeleton.lua b/spine-lua/Skeleton.lua
index dce0ec16a..c28cf29e6 100644
--- a/spine-lua/Skeleton.lua
+++ b/spine-lua/Skeleton.lua
@@ -133,7 +133,7 @@ function Skeleton.new (skeletonData)
 				return
 			end
 		end
-		error("Slot not found: " + slotName, 2)
+		error("Slot not found: " .. slotName, 2)
 	end
 
 	function self:update (delta)
diff --git a/spine-lua/SkeletonJson.lua b/spine-lua/SkeletonJson.lua
index c1b1e06b8..e5861d5c8 100755
--- a/spine-lua/SkeletonJson.lua
+++ b/spine-lua/SkeletonJson.lua
@@ -292,7 +292,7 @@ function SkeletonJson.new (attachmentLoader)
 			local frameIndex = 0
 			for i,eventMap in ipairs(events) do
 				local eventData = skeletonData:findEvent(eventMap["name"])
-				if not eventData then error("Event not found: " + eventMap["name"]) end
+				if not eventData then error("Event not found: " .. eventMap["name"]) end
 				local event = Event.new(eventData)
 				event.intValue = eventMap["int"] or eventData.intValue
 				event.floatValue = eventMap["float"] or eventData.floatValue
@@ -319,7 +319,7 @@ function SkeletonJson.new (attachmentLoader)
 					local unchangedIndex = 1
 					for ii,offsetMap in ipairs(offsets) do
 						local slotIndex = skeletonData:findSlotIndex(offsetMap["slot"])
-						if slotIndex == -1 then error("Slot not found: " + offsetMap["slot"]) end
+						if slotIndex == -1 then error("Slot not found: " .. offsetMap["slot"]) end
 						-- Collect unchanged items.
 						while originalIndex ~= slotIndex do
 							unchanged[unchangedIndex] = originalIndex