diff --git a/src/Run.hs b/src/Run.hs
index dc103c47..9ad3c086 100644
--- a/src/Run.hs
+++ b/src/Run.hs
@@ -36,12 +36,13 @@ doctest args
   | "--help"    `elem` args = putStr usage
   | "--version" `elem` args = printVersion
   | otherwise = do
-      -- Look up the PACKAGE_SANDBOX environment variable and, if present, add
-      -- it to the list of package databases GHC searches. Intended to make
-      -- testing from inside sandboxes such as cabal-dev simpler.
+      -- Look up the HASKELL_PACKAGE_SANDBOX environment variable and, if
+      -- present, add it to the list of package databases GHC searches.
+      -- Intended to make testing from inside sandboxes such as cabal-dev
+      -- simpler.
       env <- getEnvironment
       let addPackageConf =
-            case lookup "PACKAGE_SANDBOX" env of
+            case lookup "HASKELL_PACKAGE_SANDBOX" env of
               Nothing -> id
               Just p  -> \rest -> "-package-conf" : p : rest
 
diff --git a/test/RunSpec.hs b/test/RunSpec.hs
index 291f9e79..e614f1ff 100644
--- a/test/RunSpec.hs
+++ b/test/RunSpec.hs
@@ -71,7 +71,7 @@ spec = do
         , "Try `doctest --help' for more information."
         ]
 
-    it "respects PACKAGE_SANDBOX" $ do
+    it "respects HASKELL_PACKAGE_SANDBOX" $ do
       withCurrentDirectory "test/integration/custom-package-conf/foo" $ do
         ExitSuccess <- rawSystem "ghc-pkg" ["init", "../packages"]
         ExitSuccess <- rawSystem "cabal" ["configure", "--disable-optimization", "--disable-library-profiling", "--package-db=../packages"]
@@ -79,7 +79,7 @@ spec = do
         ExitSuccess <- rawSystem "cabal" ["register", "--inplace"]
         return ()
 
-      withEnv "PACKAGE_SANDBOX" "test/integration/custom-package-conf/packages" $ do
+      withEnv "HASKELL_PACKAGE_SANDBOX" "test/integration/custom-package-conf/packages" $ do
         hCapture_ [stderr] (doctest ["test/integration/custom-package-conf/Bar.hs"])
           `shouldReturn` "Examples: 2  Tried: 2  Errors: 0  Failures: 0\n"