diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for haskell-lsp
 
+## 0.2.2.0  -- 2018-05-04
+
+* Make Diagnostic relatedInformation optional, as per the LSP Spec. By @Bubba.
+
 ## 0.2.1.0  -- 2018-05-02
 
 * Broken out from the haskell-lsp package, to simplify development
diff --git a/haskell-lsp-types.cabal b/haskell-lsp-types.cabal
--- a/haskell-lsp-types.cabal
+++ b/haskell-lsp-types.cabal
@@ -1,5 +1,5 @@
 name:                haskell-lsp-types
-version:             0.2.1.0
+version:             0.2.2.0
 synopsis:            Haskell library for the Microsoft Language Server Protocol, data types
 
 description:         An implementation of the types to allow language implementors to
diff --git a/src/Language/Haskell/LSP/TH/DataTypesJSON.hs b/src/Language/Haskell/LSP/TH/DataTypesJSON.hs
--- a/src/Language/Haskell/LSP/TH/DataTypesJSON.hs
+++ b/src/Language/Haskell/LSP/TH/DataTypesJSON.hs
@@ -686,7 +686,7 @@
     , _code               :: Maybe Text -- Note: Protocol allows Int too.
     , _source             :: Maybe DiagnosticSource
     , _message            :: Text
-    , _relatedInformation :: List DiagnosticRelatedInformation
+    , _relatedInformation :: Maybe (List DiagnosticRelatedInformation)
     } deriving (Show, Read, Eq, Ord)
 
 deriveJSON lspOptions ''Diagnostic