diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,7 @@
 Changelog for Extra
 
+0.7
+    Fix for missing case in withNumCapabilities
 0.6
     Ensure barrier is thread-safe
     Make subsequent signalBarrier calls throw an exception
diff --git a/extra.cabal b/extra.cabal
--- a/extra.cabal
+++ b/extra.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.10
 build-type:         Simple
 name:               extra
-version:            0.6
+version:            0.7
 license:            BSD3
 license-file:       LICENSE
 category:           Development
diff --git a/src/Control/Concurrent/Extra.hs b/src/Control/Concurrent/Extra.hs
--- a/src/Control/Concurrent/Extra.hs
+++ b/src/Control/Concurrent/Extra.hs
@@ -37,6 +37,7 @@
     old <- getNumCapabilities
     if old == new then act else
         bracket_ (setNumCapabilities new) (setNumCapabilities old) act
+withNumCapabilities _ act = act
 
 
 #if __GLASGOW_HASKELL__ < 702