diff --git a/nselib/formulas.lua b/nselib/formulas.lua
index 916a05f1b..6f19000fa 100644
--- a/nselib/formulas.lua
+++ b/nselib/formulas.lua
@@ -70,14 +70,16 @@ local function chi2(data, num_cats)
     return x2
 end
 
+local function c_to_bin (c)
+  local n = stdnse.tobinary(c:byte())
+  return ("0"):rep(8-#n)..n
+end
+
 -- Split a string into a sequence of bit strings of the given length.
 -- splitbits("abc", 5) --> {"01100", "00101", "10001", "00110"}
 -- Any short final group is omitted.
 local function splitbits(s, n)
-    local bits = s:gsub(".", function (c)
-        local n = stdnse.tobinary(c:byte())
-        return ("0"):rep(8-#n)..n
-      end)
+    local bits = s:gsub(".", c_to_bin)
 
     local seq = {}
     for i = 1, #bits - n, n do
diff --git a/nselib/stdnse.lua b/nselib/stdnse.lua
index a800bee4f..c18013250 100644
--- a/nselib/stdnse.lua
+++ b/nselib/stdnse.lua
@@ -260,12 +260,12 @@ do
   };
 
 --- Converts the given number, n, to a string in a binary number format (12
--- becomes "1100").
+-- becomes "1100"). Leading 0s not stripped.
 -- @param n Number to convert.
 -- @return String in binary format.
   function tobinary(n)
     assert(tonumber(n), "number expected");
-    return (("%x"):format(n):gsub("%w", t):gsub("^0*", ""));
+    return (("%x"):format(n):gsub("%w", t))
   end
 end