diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 Changelog for tmp-postgres
 
+1.31.0.2
+  #230 Fix bug when the same cache is built concurrently.
+
 1.31.0.1
   #227 remove mention of defaultPostgresConf in doc
   #228 add track_io_timing = on to verboseConfig
diff --git a/src/Database/Postgres/Temp/Internal.hs b/src/Database/Postgres/Temp/Internal.hs
--- a/src/Database/Postgres/Temp/Internal.hs
+++ b/src/Database/Postgres/Temp/Internal.hs
@@ -9,6 +9,7 @@
 import Database.Postgres.Temp.Internal.Core
 import Database.Postgres.Temp.Internal.Config
 
+import           Control.Concurrent
 import qualified Control.Concurrent.Async as Async
 import           Control.DeepSeq
 import           Control.Exception
@@ -661,6 +662,9 @@
 -------------------------------------------------------------------------------
 -- cacheAction
 -------------------------------------------------------------------------------
+cacheLock :: MVar ()
+cacheLock = unsafePerformIO $ newMVar ()
+
 {-|
 Check to see if a cached data directory exists.
 
@@ -692,16 +696,18 @@
 cacheAction cachePath action config = do
   fixCachePath <- fixPath cachePath
   let result = config <> fromFilePathConfig fixCachePath
-  nonEmpty <- doesFileExist $ fixCachePath <> "/PG_VERSION"
 
-  if nonEmpty then pure $ pure result else fmap join $ withConfig config $ \db -> do
-    action db
-    -- TODO see if parallel is better
-    throwIfNotSuccess id =<< stopPostgresGracefully db
-    createDirectoryIfMissing True fixCachePath
+  withMVar cacheLock $ \_ -> do
+    nonEmpty <- doesFileExist $ fixCachePath <> "/PG_VERSION"
 
-    let snapshotCopyCmd = cpFlags <>
-          toDataDirectory db <> "/* " <> fixCachePath
-    system snapshotCopyCmd >>= \case
-      ExitSuccess -> pure $ pure result
-      x -> pure $ Left $ SnapshotCopyFailed snapshotCopyCmd x
+    if nonEmpty then pure $ pure result else fmap join $ withConfig config $ \db -> do
+      action db
+      -- TODO see if parallel is better
+      throwIfNotSuccess id =<< stopPostgresGracefully db
+      createDirectoryIfMissing True fixCachePath
+
+      let snapshotCopyCmd = cpFlags <>
+            toDataDirectory db <> "/* " <> fixCachePath
+      system snapshotCopyCmd >>= \case
+        ExitSuccess -> pure $ pure result
+        x -> pure $ Left $ SnapshotCopyFailed snapshotCopyCmd x
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -1,4 +1,5 @@
 import           Control.Concurrent
+import qualified Control.Concurrent.Async as Async
 import           Control.Exception
 import           Control.Monad ((<=<), void, unless)
 import           Data.Function
@@ -27,6 +28,7 @@
 import           System.Process
 import           System.Timeout
 import           Test.Hspec
+import           Data.Either
 
 withConn :: DB -> (PG.Connection -> IO a) -> IO a
 withConn db f = do
@@ -382,6 +384,8 @@
       either throwIO pure <=< withConfig (cacheConfig cacheInfo <> verboseConfig) $ \db -> do
         assertConnection db
         withConn db $ \conn -> countDbs conn `shouldReturn` 3
+
+
 --
 -- Error Plans. Can't be combined. Just list them out inline since they can't be combined
 --
@@ -625,6 +629,21 @@
       cacheAction theFinalCachePath action (defaultConfig { dataDirectory = Permanent theFinalCachePath } ) >>= \case
         Left (SnapshotCopyFailed {}) -> pure ()
         _ -> fail $ "cacheAction should have failed with SnapshotCopyFailed"
+
+  it "works if two threads try to create a cache at the same time" $ do
+    withTempDirectory "/tmp" "tmp-postgres-parallel-cache-test" $ \dirPath -> do
+      -- let dirPath = "/tmp/tmp-postgres-parallel-cache-test-1"
+      withDbCache $ \cacheInfo -> do
+        lock <- newEmptyMVar
+        let
+          theConfig = defaultConfig <> cacheConfig cacheInfo
+          waitIfSecond _ = do
+            tryPutMVar lock () >>= \case
+              True -> pure ()
+              False -> threadDelay 100000
+          theCacheAction = cacheAction dirPath waitIfSecond theConfig
+        res <- Async.replicateConcurrently 3 theCacheAction
+        if all isRight res then pure () else fail "Failed to create caches concurrently"
 
 spec :: Spec
 spec = do
diff --git a/tmp-postgres.cabal b/tmp-postgres.cabal
--- a/tmp-postgres.cabal
+++ b/tmp-postgres.cabal
@@ -1,5 +1,5 @@
 name:                tmp-postgres
-version:             1.31.0.1
+version:             1.31.0.2
 synopsis: Start and stop a temporary postgres
 description: Start and stop a temporary postgres. See README.md
 homepage:            https://github.com/jfischoff/tmp-postgres#readme
@@ -65,6 +65,7 @@
   hs-source-dirs:      test
   main-is:             Main.hs
   build-depends:       base
+                     , async
                      , containers
                      , directory
                      , generic-monoid