diff --git a/Cabal/src/Distribution/Simple/PackageDescription.hs b/Cabal/src/Distribution/Simple/PackageDescription.hs
index 4c64aedf767..bb7e54550c3 100644
--- a/Cabal/src/Distribution/Simple/PackageDescription.hs
+++ b/Cabal/src/Distribution/Simple/PackageDescription.hs
@@ -24,12 +24,16 @@ import Distribution.Compat.Prelude
 import Distribution.Fields.ParseResult
 import Distribution.PackageDescription
 import Distribution.PackageDescription.Parsec
-import Distribution.Parsec.Error    (showPError)
-import Distribution.Parsec.Warning  (showPWarning)
-import Distribution.Simple.Utils
-import Distribution.Verbosity
+    ( parseGenericPackageDescription, parseHookedBuildInfo )
+import Distribution.Parsec.Error ( showPError )
+import Distribution.Parsec.Warning
+    ( PWarning(..), PWarnType(PWTExperimental), showPWarning )
+import Distribution.Simple.Utils ( equating, die', warn )
+import Distribution.Verbosity ( normal, Verbosity )
 
-import qualified Data.ByteString    as BS
+import Data.List ( groupBy )
+import Text.Printf ( printf )
+import qualified Data.ByteString as BS
 import System.Directory (doesFileExist)
 
 readGenericPackageDescription :: Verbosity -> FilePath -> IO GenericPackageDescription
@@ -65,10 +69,35 @@ parseString
     -> IO a
 parseString parser verbosity name bs = do
     let (warnings, result) = runParseResult (parser bs)
-    traverse_ (warn verbosity . showPWarning name) warnings
+    traverse_ (warn verbosity . showPWarning name) (flattenDups verbosity warnings)
     case result of
         Right x -> return x
         Left (_, errors) -> do
             traverse_ (warn verbosity . showPError name) errors
             die' verbosity $ "Failed parsing \"" ++ name ++ "\"."
 
+-- Collapse duplicate experimental feature warnings into single warning, with
+-- a count of further sites
+flattenDups :: Verbosity -> [PWarning] -> [PWarning]
+flattenDups verbosity ws
+    | verbosity <= normal = rest ++ experimentals
+    | otherwise = ws -- show all instances
+    where
+        (exps, rest) = partition (\(PWarning w _ _) -> w == PWTExperimental) ws
+        experimentals =
+             concatMap flatCount
+           . groupBy (equating warningStr)
+           . sortBy (comparing warningStr)
+           $ exps
+
+        warningStr (PWarning _ _ w) = w
+
+        -- flatten if we have 3 or more examples
+        flatCount :: [PWarning] -> [PWarning]
+        flatCount w@[] = w
+        flatCount w@[_] = w
+        flatCount w@[_,_] = w
+        flatCount (PWarning t pos w:xs) =
+            [PWarning t pos
+                (w <> printf " (and %d more occurrences)" (length xs))
+            ]
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