diff --git a/src-3.0/GF/Source/SharedString.hs b/src-3.0/GF/Source/SharedString.hs
new file mode 100644
index 000000000..732873fe6
--- /dev/null
+++ b/src-3.0/GF/Source/SharedString.hs
@@ -0,0 +1,20 @@
+module GF.Source.SharedString (shareString) where
+
+import Data.Map as M
+import Data.IORef
+import qualified Data.ByteString.Char8 as BS
+import System.IO.Unsafe (unsafePerformIO)
+
+{-# NOINLINE stringPoolRef #-}
+stringPoolRef :: IORef (M.Map BS.ByteString BS.ByteString)
+stringPoolRef = unsafePerformIO $ newIORef M.empty
+
+{-# NOINLINE shareString #-}
+shareString :: BS.ByteString -> BS.ByteString
+shareString s = unsafePerformIO $ do
+  stringPool <- readIORef stringPoolRef
+  case M.lookup s stringPool of
+    Just s' -> return s'
+    Nothing -> do let s' = BS.copy s
+                  writeIORef stringPoolRef $! M.insert s' s' stringPool
+                  return s'