diff --git a/Cabal-syntax/src/Distribution/Types/PackageDescription.hs b/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
index b994f9c8813..84f31f98ef1 100644
--- a/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
+++ b/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
@@ -34,6 +34,7 @@ module Distribution.Types.PackageDescription
   , buildType
   , emptyPackageDescription
   , hasPublicLib
+  , hasPrivateDependencies
   , hasLibs
   , allLibraries
   , withLib
@@ -59,6 +60,7 @@ module Distribution.Types.PackageDescription
 
 import Distribution.Compat.Prelude
 import Prelude ()
+import qualified Data.List
 
 -- lens
 
@@ -366,6 +368,11 @@ allBuildDepends pd = do
   [(Public, d) | d <- targetBuildDepends bi]
     ++ [(Private p, d) | PrivateDependency p ds <- targetPrivateBuildDepends bi, d <- ds]
 
+-- | Does this package have any private dependencies? At the moment, cabal
+-- check will reject any packages that do.
+hasPrivateDependencies :: PackageDescription -> Bool
+hasPrivateDependencies pd = not $ Data.List.all (Data.List.null . targetPrivateBuildDepends) $ allBuildInfo pd
+
 -- | Get the combined build-depends entries of all enabled components, per the
 -- given request spec.
 enabledBuildDepends :: PackageDescription -> ComponentRequestedSpec -> [(IsPrivate, Dependency)]
diff --git a/Cabal/src/Distribution/PackageDescription/Check.hs b/Cabal/src/Distribution/PackageDescription/Check.hs
index 79123f7f9df..dc16c1bf6b7 100644
--- a/Cabal/src/Distribution/PackageDescription/Check.hs
+++ b/Cabal/src/Distribution/PackageDescription/Check.hs
@@ -428,6 +428,8 @@ checkPackageDescription
       (PackageBuildImpossible $ IllegalLibraryName pn)
 
     -- § Fields check.
+    checkP (hasPrivateDependencies pkg)
+      (PackageDistInexcusable HasPrivateDependencies)
     checkNull
       category_
       (PackageDistSuspicious MissingFieldCategory)
diff --git a/Cabal/src/Distribution/PackageDescription/Check/Warning.hs b/Cabal/src/Distribution/PackageDescription/Check/Warning.hs
index 859b3f12c50..ff430d51920 100644
--- a/Cabal/src/Distribution/PackageDescription/Check/Warning.hs
+++ b/Cabal/src/Distribution/PackageDescription/Check/Warning.hs
@@ -279,6 +279,7 @@ data CheckExplanation
   | MissingSourceControl
   | MissingExpectedDocFiles Bool [FilePath]
   | WrongFieldForExpectedDocFiles Bool String [FilePath]
+  | HasPrivateDependencies
   deriving (Eq, Ord, Show)
 
 -- TODO Some checks have a constructor in list form
@@ -441,6 +442,7 @@ data CheckExplanationID
   | CIMissingSourceControl
   | CIMissingExpectedDocFiles
   | CIWrongFieldForExpectedDocFiles
+  | CIHasPrivateDependencies
   deriving (Eq, Ord, Show, Enum, Bounded)
 
 checkExplanationId :: CheckExplanation -> CheckExplanationID
@@ -582,6 +584,7 @@ checkExplanationId (UnknownDirectory{}) = CIUnknownDirectory
 checkExplanationId (MissingSourceControl{}) = CIMissingSourceControl
 checkExplanationId (MissingExpectedDocFiles{}) = CIMissingExpectedDocFiles
 checkExplanationId (WrongFieldForExpectedDocFiles{}) = CIWrongFieldForExpectedDocFiles
+checkExplanationId (HasPrivateDependencies{}) = CIHasPrivateDependencies
 
 type CheckExplanationIDString = String
 
@@ -728,6 +731,7 @@ ppCheckExplanationId CIUnknownDirectory = "unknown-directory"
 ppCheckExplanationId CIMissingSourceControl = "no-repository"
 ppCheckExplanationId CIMissingExpectedDocFiles = "no-docs"
 ppCheckExplanationId CIWrongFieldForExpectedDocFiles = "doc-place"
+ppCheckExplanationId CIHasPrivateDependencies = "has-private-deps"
 
 -- String: the unrecognised 'CheckExplanationIDString' itself.
 readExplanationID
@@ -1460,6 +1464,15 @@ ppExplanation (WrongFieldForExpectedDocFiles extraDocFileSupport field paths) =
       if extraDocFileSupport
         then "extra-doc-files"
         else "extra-source-files"
+-- Private dependencies are a special case which must be guarded
+-- against until more extensive benchmarks regarding the performance of
+-- solving private dependencies mixed in with a lot of backtracking.
+-- See https://github.com/haskell/cabal/pull/9743
+ppExplanation HasPrivateDependencies =
+  "Private dependencies are in a feature-preview state, "
+  ++ "therefore packages using them cannot be uploaded to hackage.\n"
+  ++ "For instance, how would hackage display the private dependencies of the package?"
+
 
 -- * Formatting utilities