diff --git a/math.lua b/math.lua
index e3fa4d8..0e57dd2 100644
--- a/math.lua
+++ b/math.lua
@@ -41,7 +41,7 @@ function tostring(number, base, digit_function, precision)
 	while number >= base do
 		digit = math.floor(number % base)
 		table.insert(out, digit_function(digit))
-		number = number / base
+		number = (number - digit) / base
 	end
 	digit = math.floor(number)
 	table.insert(out, digit_function(digit))
@@ -49,7 +49,7 @@ function tostring(number, base, digit_function, precision)
 	number = number % 1
 	if number ~= 0 and number >= base ^ -precision then
 		table.insert(out, ".")
-		while precision >= 0 and number >= base ^ precision do
+		while precision >= 0 and number >= base ^ -precision do
 			number = number * base
 			digit = math.floor(number % base)
 			table.insert(out, digit_function(digit))
diff --git a/test.lua b/test.lua
index 7e45f35..9f0fceb 100644
--- a/test.lua
+++ b/test.lua
@@ -16,6 +16,16 @@ setfenv(1, setmetatable({}, {
 	end
 }))
 
+-- math
+do
+	local function assert_tonumber(num, base)
+		local str = modlib.math.tostring(num, base)
+		assert(tonumber(str, base) == num, str)
+	end
+	assert_tonumber(134217503, 36)
+	assert_tonumber(3.14, 10)
+end
+
 -- func
 do
 	local tab = {a = 1, b = 2}