diff --git a/Library/Homebrew/extend/kernel.rb b/Library/Homebrew/extend/kernel.rb
index 94bcf520c0..7d21851fd0 100644
--- a/Library/Homebrew/extend/kernel.rb
+++ b/Library/Homebrew/extend/kernel.rb
@@ -459,13 +459,13 @@ module Kernel
   end
 
   def disk_usage_readable(size_in_bytes)
-    if size_in_bytes >= 1_073_741_824
+    if size_in_bytes.abs >= 1_073_741_824
       size = size_in_bytes.to_f / 1_073_741_824
       unit = "GB"
-    elsif size_in_bytes >= 1_048_576
+    elsif size_in_bytes.abs >= 1_048_576
       size = size_in_bytes.to_f / 1_048_576
       unit = "MB"
-    elsif size_in_bytes >= 1_024
+    elsif size_in_bytes.abs >= 1_024
       size = size_in_bytes.to_f / 1_024
       unit = "KB"
     else