diff --git a/servant-server/test/Doctests.hs b/servant-server/test/Doctests.hs
index 5bf9c91f..71d1d2c2 100644
--- a/servant-server/test/Doctests.hs
+++ b/servant-server/test/Doctests.hs
@@ -27,3 +27,5 @@ getCabalMacrosFile = do
   return $ case filter ("dist-sandbox-" `isPrefixOf`) contents of
     [x] -> "dist" </> x </> rest
     [] -> "dist" </> rest
+    xs -> error $ "ran doctests with multiple dist/dist-sandbox-xxxxx's: \n"
+                ++ show xs ++ "\nTry cabal clean"
diff --git a/servant/test/Doctests.hs b/servant/test/Doctests.hs
index 63d842f0..eb3f688c 100644
--- a/servant/test/Doctests.hs
+++ b/servant/test/Doctests.hs
@@ -25,3 +25,5 @@ getCabalMacrosFile = do
   return $ case filter ("dist-sandbox-" `isPrefixOf`) contents of
     [x] -> "dist" </> x </> rest
     [] -> "dist" </> rest
+    xs -> error $ "ran doctests with multiple dist/dist-sandbox-xxxxx's: \n"
+                ++ show xs ++ "\nTry cabal clean"