diff --git a/scripts.lua b/scripts.lua
index 5fd84c8..5d60e78 100644
--- a/scripts.lua
+++ b/scripts.lua
@@ -19,7 +19,7 @@ function split_fmt(f)
                 in_spec = false
                 curr = ""
             elseif string.match(char, '[qs]') then
-                if string.match(curr, '^%%[0-9]*$') then
+                if string.match(curr, '^%%%-?[0-9]*$') then
                     curr = curr .. char
                     table.insert(ret, curr)
                     in_spec = false
@@ -28,7 +28,7 @@ function split_fmt(f)
                     io.stderr:write("Invalid format:  '" .. curr .. char .. "'\n")
                     return nil
                 end
-            elseif string.match(char, '[0-9%.]') then
+            elseif string.match(char, '[0-9%.%-]') then
                 curr = curr .. char
             elseif string.match(char, '%%') then
                 if string.match(curr, '^%%') then
@@ -105,7 +105,7 @@ function conky_printf(format, ...)
     end
     for i,fs in ipairs(formats) do
         if is_fmt_spec(fs) then -- we have a format specifier
-            if string.match(fs, '[dEefgiouXx]$') then -- we have a numeric format specifier, convert value to number
+            if string.match(fs, '[cdEefgiouXx]$') then -- we have a numeric format specifier, convert value to number
                 parsed_values[i] = tonumber(trim((parsed_values[i])))
             end
         end