diff --git a/InputStream.tl b/InputStream.tl
index 1a91a07..4d8db6a 100644
--- a/InputStream.tl
+++ b/InputStream.tl
@@ -3,7 +3,6 @@ local type InputStream = record
 	offset: number
 	refill: function(): string
 
-	new: function(InputStream): InputStream
 	new: function(InputStream, function(): string): InputStream
 
 	setRefill: function(InputStream, function(): string)
@@ -19,28 +18,36 @@ function InputStream:_manageBuffer()
 		self.str = self.refill()
 		self.offset = 1
 	end
-	if self.offset > #self.str + 1 then
+	if self.offset > #self.str then
 		self.str = self.refill()
 		self.offset = 1
 	end
 end
 
+local function initial_stream(): string
+	return "DUMMY"
+end
 
 
 -- constructors
 function InputStream:new(): InputStream
-	return setmetatable(
-		{
-			string = "",
-			offset = 1
-		} as InputStream,
-		istream_mt)
-end
-function InputStream:new(refill: function(): string): InputStream
 	local mt = setmetatable(
 		{
 			string = "",
-			offset = 1
+			offset = 1,
+			refill = initial_stream
+		} as InputStream,
+		istream_mt)
+	mt:setRefill(initial_stream)
+	return mt
+end
+function InputStream:new(refill: function(): string): InputStream
+	refill = refill or initial_stream
+	local mt = setmetatable(
+		{
+			string = "",
+			offset = 1,
+			refill = function(): string return "DUMMY" end
 		} as InputStream,
 		istream_mt)
 	mt:setRefill(refill)
@@ -53,6 +60,7 @@ end
 -- setters/getters
 function InputStream:setRefill(func: function(): string)
 	self.refill = func
+	self:_manageBuffer()
 end
 
 -- 
@@ -62,9 +70,9 @@ function InputStream:readCurrentCharacter(): string
 end
 
 function InputStream:advanceOffset(): string
+	self:_manageBuffer()
 	local current_char = self.str:sub(self.offset, self.offset)
 	self.offset = self.offset + 1
-	self:_manageBuffer()
 	return current_char
 end