diff --git a/bigint.lua b/bigint.lua
index b750539..7ca18f7 100644
--- a/bigint.lua
+++ b/bigint.lua
@@ -207,6 +207,17 @@ local function udec(a)
     trim(a)
 end
 
+local function upow(a, b)
+    -- https://stackoverflow.com/a/102319/2332397
+    if #b == 1 and b[1] == 0 then return BigInt(1) end
+    local temp = upow(a, b/2)
+    if b[1] % 2 == 0 then
+        return temp * temp
+    else
+        return a * temp * temp
+    end
+end
+
 function BigInt.__eq(a, b)
     if #a ~= #b then return false end
     if a.sign ~= b.sign then return false end
@@ -289,6 +300,8 @@ function BigInt.__mul(a, b)
 end
 
 function BigInt.__div(a, b)
+    local a = BigInt(a)
+    local b = BigInt(b)
     local q = udiv(a, b)
     q.sign = a.sign * b.sign
     trim(q)
@@ -297,15 +310,8 @@ end
 
 function BigInt.__pow(a, b)
     local a = BigInt(a)
-    local b = BigInt(b):clone()
-    local c = BigInt(1)
-    local i = BigInt(1)
-    if b.sign == -1 then b.sign = 1 end
-    while i <= b do
-        c = c * a
-        i:inc()
-    end
-    return c
+    local b = BigInt(b)
+    return upow(a, b)
 end
 
 function BigInt:__tostring()