diff --git a/pretty.lua b/pretty.lua
index e5a4ee4..c2a244f 100644
--- a/pretty.lua
+++ b/pretty.lua
@@ -104,9 +104,8 @@ local VALUE_TYPE_SORT_ORDER = {
 --------------------------------------------------------------------------------
 -- Key-value-pair Util
 
-local function padnum(d)
-    local dec, n = string.match(d, "(%.?)0*(.+)")
-    return #dec > 0 and ("%.12f"):format(d) or ("%s%03d%s"):format(dec, #n, n)
+local function padnum(minus, dec, zeroes, n)
+    return dec == '.' and ("%.12f"):format(dec..zeroes..n) or ("%s%03d%s"):format(minus == '' and ':' or minus, #n, n)
 end
 
 local function alphanum_compare_strings (a, b)
@@ -115,8 +114,13 @@ local function alphanum_compare_strings (a, b)
     assert(type(a) == 'string')
     assert(type(b) == 'string')
 
-    local a_padded  =  a:gsub("%.?%d+", padnum)..("\0%3d"):format(#b)
-    local b_padded  =  b:gsub("%.?%d+", padnum)..("\0%3d"):format(#a)
+    local a_padded  =  a:gsub("(%-?)(%.?)(0*)(%d+)", padnum)..("\0%3d"):format(#b)
+    local b_padded  =  b:gsub("(%-?)(%.?)(0*)(%d+)", padnum)..("\0%3d"):format(#a)
+    -- Correction for sorting of negative numbers:
+    if a_padded:sub(1,1) == '-' and b_padded:sub(1,1) == '-' then
+        a_padded, b_padded = b_padded, a_padded
+    end
+    --
     local A_padded, B_padded  =  a_padded:upper(), b_padded:upper()
     if A_padded == B_padded then  return  a_padded < b_padded  end
     return A_padded < B_padded
diff --git a/test/test_sorting.lua b/test/test_sorting.lua
index 1b3a0d2..6292087 100644
--- a/test/test_sorting.lua
+++ b/test/test_sorting.lua
@@ -87,8 +87,8 @@ format_test {
 
 format_test {
 	name   = 'Proper sorting of number strings keys',
-    input  = { ['-100'] = 'a', ['-1'] = 'b', ['0'] = 'c', ['1'] = 'd', ['100'] = 'e' },
-    expect = '{\n    [\'-100\'] = \'b\',  [\'-1\']   = \'c\',\n    [\'0\']    = \'d\',  [\'1\']    = \'e\',\n    [\'100\']  = \'f\'\n}',
+    input  = { ['-10'] = 'a', ['-0.5'] = 'b', ['0'] = 'c', ['1'] = 'd', ['10.1'] = 'e' },
+    expect = '{\n    [\'-10\']  = \'a\',  [\'-0.5\'] = \'b\',\n    [\'0\']    = \'c\',  [\'1\']    = \'d\',\n    [\'10.1\'] = \'e\'\n}',
 }