diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,13 @@
 # ChangeLog for resourcet
 
+## 1.2.4.1
+
+* Document risk of using `forkIO` within a `ResourceT` [#441](https://github.com/snoyberg/conduit/pull/441)
+
+## 1.2.4
+
+* Add `allocate_` [#437](https://github.com/snoyberg/conduit/pull/437)
+
 ## 1.2.3
 
 * Support `unliftio-core` 0.2.0.0
diff --git a/Control/Monad/Trans/Resource.hs b/Control/Monad/Trans/Resource.hs
--- a/Control/Monad/Trans/Resource.hs
+++ b/Control/Monad/Trans/Resource.hs
@@ -265,6 +265,14 @@
 --
 -- This is defined as @resourceForkWith forkIO@.
 --
+-- Note: Using regular 'forkIO' inside of a 'ResourceT' is inherently unsafe,
+-- since the forked thread may try access the resources of the parent after they are cleaned up.
+-- When you use 'resourceForkIO' or 'resourceForkWith', 'ResourceT' is made aware of the new thread, and will only cleanup resources when all threads finish.
+-- Other concurrency mechanisms, like 'concurrently' or 'race', are safe to use.
+--
+-- If you encounter 'InvalidAccess' exceptions ("The mutable state is being accessed after cleanup"),
+-- use of 'forkIO' is a possible culprit.
+--
 -- @since 0.3.0
 resourceForkIO :: MonadUnliftIO m => ResourceT m () -> ResourceT m ThreadId
 resourceForkIO = resourceForkWith forkIO
diff --git a/resourcet.cabal b/resourcet.cabal
--- a/resourcet.cabal
+++ b/resourcet.cabal
@@ -1,5 +1,5 @@
 Name:                resourcet
-Version:             1.2.4
+Version:             1.2.4.1
 Synopsis:            Deterministic allocation and freeing of scarce resources.
 description:         Hackage documentation generation is not reliable. For up to date documentation, please see: <http://www.stackage.org/package/resourcet>.
 License:             BSD3
@@ -8,11 +8,12 @@
 Maintainer:          michael@snoyman.com
 Category:            Data, Conduit
 Build-type:          Simple
-Cabal-version:       >=1.8
+Cabal-version:       >=1.10
 Homepage:            http://github.com/snoyberg/conduit
 extra-source-files:  ChangeLog.md, README.md
 
 Library
+  default-language:    Haskell2010
   Exposed-modules:     Control.Monad.Trans.Resource
                        Control.Monad.Trans.Resource.Internal
                        Data.Acquire
@@ -28,6 +29,7 @@
   ghc-options:     -Wall
 
 test-suite test
+    default-language:    Haskell2010
     hs-source-dirs: test
     main-is: main.hs
     type: exitcode-stdio-1.0