diff --git a/Main.hs b/Main.hs
index 56a814d..bb151c1 100644
--- a/Main.hs
+++ b/Main.hs
@@ -61,6 +61,7 @@ options =
   , Option ['v'] ["verbose"] (NoArg $ optVerbose) "be more verbose (use multiple times for more detail)"
   , Option ['o'] ["output"] (ReqArg optOutput "FILE") "output file (default \"-\")"
   , Option [] ["usage-checking"] (ReqArg optUsageChecking "SETTING") "usage checking (EXPERIMENTAL) (options: on, off)"
+  , Option [] ["sanity-check"] (ReqArg optSanityCheck "SETTING") "internal sanity check (options: on, off)"
   ]
 
 optMode :: String -> OptFunc
@@ -105,6 +106,14 @@ optUsageChecking s ps
             _ -> dieIO (Nothing, "Unknown usage checking mode: " ++ s)
           return $ ps { csUsageChecking = usageCheck }
 
+optSanityCheck :: String -> OptFunc
+optSanityCheck s ps
+    =  do sanityCheck <- case s of
+            "on" -> return True
+            "off" -> return False
+            _ -> dieIO (Nothing, "Unknown sanity checking mode: " ++ s)
+          return $ ps { csSanityCheck = sanityCheck }
+
 getOpts :: [String] -> IO ([OptFunc], [String])
 getOpts argv =
   case getOpt RequireOrder options argv of
diff --git a/common/CompState.hs b/common/CompState.hs
index c5506ce..1d9a1f9 100644
--- a/common/CompState.hs
+++ b/common/CompState.hs
@@ -57,6 +57,7 @@ data CompState = CompState {
     csMode :: CompMode,
     csBackend :: CompBackend,
     csFrontend :: CompFrontend,
+    csSanityCheck :: Bool,
     csUsageChecking :: Bool,
     csVerboseLevel :: Int,
     csOutputFile :: String,
@@ -89,6 +90,7 @@ emptyState = CompState {
     csMode = ModeFull,
     csBackend = BackendC,
     csFrontend = FrontendOccam,
+    csSanityCheck = False,
     csUsageChecking = False, -- For now!  TODO turn this on by default
     csVerboseLevel = 0,
     csOutputFile = "-",
diff --git a/common/PassList.hs b/common/PassList.hs
index b2a2bda..6e33cf1 100644
--- a/common/PassList.hs
+++ b/common/PassList.hs
@@ -69,8 +69,9 @@ getPassList optsPS = filterPasses optsPS $ concat
 
 calculatePassList :: (Die m, CSMR m) => m [Pass]
 calculatePassList
-  = do rawList <- getCompState >>* getPassList
-       case buildGraph rawList of
+  = do st <- getCompState
+       let rawList = getPassList st
+       case buildGraph (csSanityCheck st) rawList of
          Left err -> dieReport (Nothing, "Error working out pass list: " ++ err)
          Right g -> return $ graphToList (g :: Gr Pass ())
 
@@ -82,8 +83,9 @@ calculatePassList
 graphToList :: Graph gr => gr Pass () -> [Pass]
 graphToList = topsort'
 
-buildGraph :: forall gr. Graph gr => [Pass] -> Either String (gr Pass ())
-buildGraph passes = do checked <- checkedRelations
+buildGraph :: forall gr. Graph gr => Bool -> [Pass] -> Either String (gr Pass ())
+buildGraph runProps passes
+                  = do checked <- checkedRelations
                        checkPassUnique
                        checkGraph
                        nodes <- labelledNodes
@@ -98,7 +100,7 @@ buildGraph passes = do checked <- checkedRelations
   
     propToPass :: Property -> Pass
     propToPass prop = Pass {
-      passCode = runPassR (\t -> propCheck prop t >> return t)
+      passCode = if runProps then runPassR (\t -> propCheck prop t >> return t) else return
      ,passName = prefixPropName (propName prop)
      ,passPre  = Set.empty
      ,passPost = Set.empty