diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -30,8 +30,11 @@
   ```shell
   cd mypackage
   npm init .
-  npm install --save serverless serverless-haskell
+  npm install --save serverless serverless-haskell@x.y.z
   ```
+
+  The version of the NPM package to install must match the version of the
+  Haskell package.
 
 * Create `serverless.yml` with the following contents:
 
diff --git a/serverless-haskell.cabal b/serverless-haskell.cabal
--- a/serverless-haskell.cabal
+++ b/serverless-haskell.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: de3ca0521fac10e02fd1ab8bb6c9faa99c7d3f9d60cd1618717f00e7eaa114f8
+-- hash: ac843bed637b21c8674b64d5c6378640178701a7e162c5ded08d7b2c85da1fef
 
 name:           serverless-haskell
-version:        0.6.3
+version:        0.6.4
 synopsis:       Deploying Haskell code onto AWS Lambda using Serverless
 description:    Utilities to help process the events from AWS Lambda when deployed with the serverless-haskell plugin.
 category:       AWS, Cloud, Network
diff --git a/src/AWSLambda.hs b/src/AWSLambda.hs
--- a/src/AWSLambda.hs
+++ b/src/AWSLambda.hs
@@ -10,42 +10,45 @@
 To deploy a Haskell function on AWS Lambda:
 
 * Initialise a Serverless project in the same directory as your Stack-enabled
-  package and install the @serverless-haskell@ plugin:
+package and install the @serverless-haskell@ plugin:
 
-  > npm init .
-  > npm install --save serverless serverless-haskell
+    > npm init .
+    > npm install --save serverless serverless-haskell@x.y.z
 
+    The version of the NPM package to install must match the version of the
+    Haskell package.
+
 * Create @serverless.yml@ with the following contents:
 
-  > service: myservice
-  >
-  > provider:
-  >   name: aws
-  >   runtime: nodejs8.10
-  >
-  > functions:
-  >   myfunc:
-  >     handler: mypackage.mypackage-exe
-  >     # Here, mypackage is the Haskell package name and mypackage-exe is the
-  >     # executable name as defined in the Cabal file
-  >
-  > plugins:
-  >   - serverless-haskell
+    > service: myservice
+    >
+    > provider:
+    >   name: aws
+    >   runtime: nodejs8.10
+    >
+    > functions:
+    >   myfunc:
+    >     handler: mypackage.mypackage-exe
+    >     # Here, mypackage is the Haskell package name and mypackage-exe is the
+    >     # executable name as defined in the Cabal file
+    >
+    > plugins:
+    >   - serverless-haskell
 
 * Write your @main@ function using 'AWSLambda.lambdaMain'.
 
 * Use @sls deploy@ to deploy the executable to AWS Lambda. __Note__: @sls deploy
-  function@ is
-  <https://github.com/seek-oss/serverless-haskell/issues/20 not supported yet>.
+function@ is
+<https://github.com/seek-oss/serverless-haskell/issues/20 not supported yet>.
 
-  The @serverless-haskell@ plugin will build the package using Stack and upload
-  it to AWS together with a JavaScript wrapper to pass the input and output
-  from/to AWS Lambda.
+    The @serverless-haskell@ plugin will build the package using Stack and upload
+    it to AWS together with a JavaScript wrapper to pass the input and output
+    from/to AWS Lambda.
 
-  You can test the function and see the invocation results with @sls invoke
-  myfunc@.
+    You can test the function and see the invocation results with @sls invoke
+    myfunc@.
 
-  To invoke the function locally, use @sls invoke local -f myfunc@.
+    To invoke the function locally, use @sls invoke local -f myfunc@.
 
 = API Gateway
 
@@ -62,37 +65,37 @@
 section of @serverless.yml@.
 
 * To add flags to @stack build@, specify them as an array under
-  @stackBuildArgs@:
+@stackBuildArgs@:
 
-  > custom:
-  >   haskell:
-  >     stackBuildArgs:
-  >       - --pedantic
-  >       - --allow-different-user
+    > custom:
+    >   haskell:
+    >     stackBuildArgs:
+    >       - --pedantic
+    >       - --allow-different-user
 
 * To start the executable with extra arguments, add them to @arguments@ under
-  the function name:
+the function name:
 
-  > custom:
-  >   haskell:
-  >     arguments:
-  >       myfunc:
-  >         - --arg1
-  >         - --arg2
-  >         - arg3
+    > custom:
+    >   haskell:
+    >     arguments:
+    >       myfunc:
+    >         - --arg1
+    >         - --arg2
+    >         - arg3
 
 * Dependent system libraries not present in the AWS Lambda environment will be
-  automatically uploaded along with the executable. Note that while statically
-  linking the executable via Cabal options is possible, it might still require
-  the corresponding glibc version on the AWS environment.
+automatically uploaded along with the executable. Note that while statically
+linking the executable via Cabal options is possible, it might still require
+the corresponding glibc version on the AWS environment.
 
 * To force using Stack's Docker image, set @docker@ key to @true@. It is
-  recommended to set this to avoid incompatibility issues with dependent system
-  libraries.
+recommended to set this to avoid incompatibility issues with dependent system
+libraries.
 
-  > custom:
-  >   haskell:
-  >     docker: true
+    > custom:
+    >   haskell:
+    >     docker: true
 -}
 module AWSLambda
   ( Handler.lambdaMain