diff --git a/Cabal.cabal b/Cabal.cabal
--- a/Cabal.cabal
+++ b/Cabal.cabal
@@ -1,5 +1,5 @@
 Name: Cabal
-Version: 1.8.0.4
+Version: 1.8.0.6
 Copyright: 2003-2006, Isaac Jones
            2005-2009, Duncan Coutts
 License: BSD3
@@ -32,7 +32,7 @@
 source-repository this
   type:     darcs
   location: http://darcs.haskell.org/cabal-branches/cabal-1.8/
-  tag: 1.8.0.4
+  tag: 1.8.0.6
 
 Flag base4
     Description: Choose the even newer, even smaller, split-up base package.
@@ -59,7 +59,7 @@
   ghc-options: -Wall -fno-ignore-asserts
   if impl(ghc >= 6.8)
     ghc-options: -fwarn-tabs
-  cpp-options: "-DCABAL_VERSION=1,8,0,4"
+  cpp-options: "-DCABAL_VERSION=1,8,0,6"
   nhc98-Options: -K4M
 
   Exposed-Modules:
diff --git a/Distribution/Simple/Register.hs b/Distribution/Simple/Register.hs
--- a/Distribution/Simple/Register.hs
+++ b/Distribution/Simple/Register.hs
@@ -115,7 +115,7 @@
 import Control.Monad (when)
 import Data.Maybe
          ( isJust, fromMaybe, maybeToList )
-import Data.List (partition)
+import Data.List (partition, nub)
 
 
 -- -----------------------------------------------------------------------------
@@ -146,8 +146,11 @@
     modeGenerateRegScript = fromFlag (regGenScript regFlags)
 
     inplace   = fromFlag (regInPlace regFlags)
-    packageDbs = withPackageDB lbi
-              ++ maybeToList (flagToMaybe  (regPackageDB regFlags))
+    -- FIXME: there's really no guarantee this will work.
+    -- registering into a totally different db stack can
+    -- fail if dependencies cannot be satisfied.
+    packageDbs = nub $ withPackageDB lbi
+                    ++ maybeToList (flagToMaybe  (regPackageDB regFlags))
     distPref  = fromFlag (regDistPref regFlags)
     verbosity = fromFlag (regVerbosity regFlags)