diff --git a/etc/diskspace/remove-old-stack-work-libs.hs b/etc/diskspace/remove-old-stack-work-libs.hs
index 2a85942e..a2cd4e3b 100755
--- a/etc/diskspace/remove-old-stack-work-libs.hs
+++ b/etc/diskspace/remove-old-stack-work-libs.hs
@@ -28,8 +28,9 @@ main = do
 
     extractNameInternal :: String -> String
     extractNameInternal p =
-      let (name,_,internal) = p =~ "-[0-9.]+-[0-9A-Za-z]{20,22}" :: (String, String, String)
-      in name ++ internal
+      let (name,match,internal) = p =~ "-[0-9.]+-[0-9A-Za-z]{20,22}" :: (String, String, String)
+      in if null match || null name then error $ p ++ " not in correct name-version-hash format"
+         else name ++ internal
 
     samePkgDynLib d1 d2 = pkgDynName d1 == pkgDynName d2
       where