diff --git a/shellcheck.hs b/shellcheck.hs
index 4e8a155..6be9bb1 100644
--- a/shellcheck.hs
+++ b/shellcheck.hs
@@ -396,7 +396,7 @@ ioInterface options files = do
     inputs <- mapM normalize files
     cache <- newIORef emptyCache
     configCache <- newIORef ("", Nothing)
-    return SystemInterface {
+    return (newSystemInterface :: SystemInterface IO) {
         siReadFile = get cache inputs,
         siFindSource = findSourceFile inputs (sourcePaths options),
         siGetConfig = getConfig configCache
diff --git a/src/ShellCheck/Interface.hs b/src/ShellCheck/Interface.hs
index 7528559..077212f 100644
--- a/src/ShellCheck/Interface.hs
+++ b/src/ShellCheck/Interface.hs
@@ -39,11 +39,12 @@ module ShellCheck.Interface
     , ColorOption(ColorAuto, ColorAlways, ColorNever)
     , TokenComment(tcId, tcComment, tcFix)
     , emptyCheckResult
-    , newParseResult
-    , newAnalysisSpec
     , newAnalysisResult
+    , newAnalysisSpec
     , newFormatterOptions
+    , newParseResult
     , newPosition
+    , newSystemInterface
     , newTokenComment
     , mockedSystemInterface
     , mockRcFile
@@ -135,6 +136,14 @@ newParseSpec = ParseSpec {
     psShellTypeOverride = Nothing
 }
 
+newSystemInterface :: Monad m => SystemInterface m
+newSystemInterface =
+    SystemInterface {
+        siReadFile = \_ _ -> return $ Left "Not implemented",
+        siFindSource = \_ _ _ name -> return name,
+        siGetConfig = \_ -> return Nothing
+    }
+
 -- Parser input and output
 data ParseSpec = ParseSpec {
     psFilename :: String,
@@ -311,7 +320,7 @@ data ColorOption =
 
 -- For testing
 mockedSystemInterface :: [(String, String)] -> SystemInterface Identity
-mockedSystemInterface files = SystemInterface {
+mockedSystemInterface files = (newSystemInterface :: SystemInterface Identity) {
     siReadFile = rf,
     siFindSource = fs,
     siGetConfig = const $ return Nothing