diff --git a/Main.hs b/Main.hs
index dba438f..e8bb446 100644
--- a/Main.hs
+++ b/Main.hs
@@ -73,6 +73,7 @@ optionsNoWarnings =
   , Option [] ["external-link"] (ReqArg optCompilerLinkFlags "FLAGS") "link flags for C/C++ compiler"
   , Option [] ["run-indent"] (NoArg $ optRunIndent) "run indent on source before compilation (will full mode)"
   , Option [] ["frontend"] (ReqArg optFrontend "FRONTEND") "language frontend (options: occam, rain)"
+  , Option ['u'] ["implicit-module"] (ReqArg optImplicitModule "MODULE") "implicitly use this module"
   , Option [] ["include-path"] (NoArg $ optPrintPath tockIncludeDir) "print include path"
   , Option [] ["lib-path"] (NoArg $ optPrintPath tockLibDir) "print lib path"
   , Option [] ["mode"] (ReqArg optMode "MODE") "select mode (options: flowgraph, lex, html, parse, compile, post-c, full)"
@@ -136,6 +137,9 @@ optSearchPath s ps = return $ ps { csSearchPath = csSearchPath ps ++ splitOnColo
       (p, _:more) -> p : splitOnColons more
       (p, []) -> [p]
 
+optImplicitModule :: String -> OptFunc
+optImplicitModule s ps = return $ ps { csImplicitModules = csImplicitModules ps ++ [s] }
+
 optCompilerFlags :: String -> OptFunc
 optCompilerFlags flags ps = return $ ps { csCompilerFlags = flags ++ " " ++ csCompilerFlags ps}
 
diff --git a/data/CompState.hs b/data/CompState.hs
index 0b63bc7..e21c61b 100644
--- a/data/CompState.hs
+++ b/data/CompState.hs
@@ -119,6 +119,7 @@ data CompState = CompState {
     csClassicOccamMobility :: Bool,
     csUnknownStackSize :: Integer,
     csSearchPath :: [String],
+    csImplicitModules :: [String],
 
     -- Set by preprocessor
     csCurrentFile :: String, -- Also used by some later passes!
@@ -181,6 +182,7 @@ emptyState = CompState {
     csClassicOccamMobility = False,
     csUnknownStackSize = 512,
     csSearchPath = [".", tockIncludeDir],
+    csImplicitModules = [],
 
     csCurrentFile = "none",
     csUsedFiles = Set.empty,
diff --git a/frontends/PreprocessOccam.hs b/frontends/PreprocessOccam.hs
index 73aff21..33678ce 100644
--- a/frontends/PreprocessOccam.hs
+++ b/frontends/PreprocessOccam.hs
@@ -42,8 +42,8 @@ import StructureOccam
 import Utils
 
 -- | Preprocess a file and return its tokenised form ready for parsing.
-preprocessFile :: Meta -> String -> PassM [Token]
-preprocessFile m filename
+preprocessFile :: Meta -> [String] -> String -> PassM [Token]
+preprocessFile m implicitMods filename
     =  do (handle, realFilename) <- searchFile m filename
           progress $ "Loading source file " ++ realFilename
           origCS <- get
@@ -54,7 +54,7 @@ preprocessFile m filename
           modify (\cs -> cs { csCurrentFile = realFilename
                             , csUsedFiles = modFunc $ csUsedFiles cs })
           s <- liftIO $ hGetContents handle
-          toks <- preprocessSource m realFilename s
+          toks <- preprocessSource m implicitMods realFilename s
           modify (\cs -> cs { csCurrentFile = csCurrentFile origCS })
           return toks
   where
@@ -62,13 +62,13 @@ preprocessFile m filename
     drop9 = reverse . drop 9 . reverse
 
 -- | Preprocesses source directly and returns its tokenised form ready for parsing.
-preprocessSource :: Meta -> String -> String -> PassM [Token]
-preprocessSource m realFilename s
+preprocessSource :: Meta -> [String] -> String -> String -> PassM [Token]
+preprocessSource m implicitMods realFilename s
     =  do toks <- runLexer realFilename $ removeASM s
           veryDebug $ "{{{ lexer tokens"
           veryDebug $ pshow toks
           veryDebug $ "}}}"
-          toks' <- preprocessOccam toks
+          toks' <- preprocessOccam $ incImplicit ++ toks
           veryDebug $ "{{{ preprocessed tokens"
           veryDebug $ pshow toks'
           veryDebug $ "}}}"
@@ -78,6 +78,11 @@ preprocessSource m realFilename s
           veryDebug $ "}}}"
           expandIncludes toks''
   where
+    incImplicit = concat [[Token emptyMeta $ TokPreprocessor $ "#USE \"" ++ f ++ "\""
+--                          ,Token emptyMeta EndOfLine
+                          ]
+                         | f <- implicitMods]
+    
     --ASM blocks tend to screw up the lexer.  Tock is unlikely to support them
     -- any time soon, but at the same time lots of occam code does have ASM blocks,
     -- and even if they are inside a #IFDEF, it will still cause Tock to choke
@@ -119,7 +124,7 @@ preprocessSource m realFilename s
 expandIncludes :: [Token] -> PassM [Token]
 expandIncludes [] = return []
 expandIncludes (Token m (IncludeFile filename) : Token _ EndOfLine : ts)
-    =  do contents <- preprocessFile m filename
+    =  do contents <- preprocessFile m [] filename
           rest <- expandIncludes ts
           return $ contents ++ rest
 expandIncludes (Token m (IncludeFile _) : _)
@@ -414,7 +419,8 @@ runPreprocParser m prod s
 -- | Load and preprocess an occam program.
 preprocessOccamProgram :: String -> PassM [Token]
 preprocessOccamProgram filename
-    =  do toks <- preprocessFile emptyMeta filename
+    =  do mods <- getCompState >>* csImplicitModules
+          toks <- preprocessFile emptyMeta mods filename
           -- Leave the main file name in the csCurrentFile slot:
           modify $ \cs -> cs { csCurrentFile = filename }
           veryDebug $ "{{{ tokenised source"
@@ -424,4 +430,4 @@ preprocessOccamProgram filename
 
 -- | Preprocesses occam source direct from the given String
 preprocessOccamSource :: String -> PassM [Token]
-preprocessOccamSource source = preprocessSource emptyMeta "<unknown>" source
+preprocessOccamSource source = preprocessSource emptyMeta [] "<unknown>" source