diff --git a/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs b/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
index b98d493656c..16fbcf51610 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
@@ -12,6 +12,7 @@ module Distribution.Solver.Types.ProjectConfigPath
     , docProjectConfigPath
     , docProjectConfigPaths
     , cyclicalImportMsg
+    , duplicateImportMsg
     , docProjectConfigPathFailReason
 
     -- * Checks and Normalization
@@ -102,13 +103,24 @@ docProjectConfigPaths :: [ProjectConfigPath] -> Doc
 docProjectConfigPaths ps = vcat
     [ text "-" <+> text p | ProjectConfigPath (p :| _) <- ps ]
 
--- | A message for a cyclical import, assuming the head of the path is the
--- duplicate.
+-- | A message for a cyclical import, a "cyclical import of".
 cyclicalImportMsg :: ProjectConfigPath -> Doc
-cyclicalImportMsg path@(ProjectConfigPath (duplicate :| _)) =
+cyclicalImportMsg path@(ProjectConfigPath (duplicate :| _)) = seenImportMsg "cyclical" duplicate path []
+
+-- | A message for a duplicate import, a "duplicate import of".
+duplicateImportMsg :: FilePath -> ProjectConfigPath -> [(FilePath, ProjectConfigPath)] -> Doc
+duplicateImportMsg = seenImportMsg "duplicate"
+
+seenImportMsg :: String -> FilePath -> ProjectConfigPath -> [(FilePath, ProjectConfigPath)] -> Doc
+seenImportMsg seen duplicate path seenImportsBy =
     vcat
-    [ text "cyclical import of" <+> text duplicate <> semi
+    [ text seen <+> text "import of" <+> text duplicate <> semi
     , nest 2 (docProjectConfigPath path)
+    , nest 2 $
+        vcat
+        [ docProjectConfigPath dib
+        | (_, dib) <- filter ((duplicate ==) . fst) seenImportsBy
+        ]
     ]
 
 docProjectConfigPathFailReason :: VR -> ProjectConfigPath -> Doc
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 49720fdd8ea..72f527cf35d 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -33,6 +34,7 @@ module Distribution.Client.ProjectConfig.Legacy
   ) where
 
 import Data.Coerce (coerce)
+import Data.IORef
 import Distribution.Client.Compat.Prelude
 
 import Distribution.Types.Flag (FlagName, parsecFlagAssignment)
@@ -137,7 +139,8 @@ import Distribution.Types.CondTree
   )
 import Distribution.Types.SourceRepo (RepoType)
 import Distribution.Utils.NubList
-  ( fromNubList
+  ( NubList
+  , fromNubList
   , overNubList
   , toNubList
   )
@@ -244,13 +247,16 @@ parseProject
 parseProject rootPath cacheDir httpTransport verbosity configToParse = do
   let (dir, projectFileName) = splitFileName rootPath
   projectDir <- makeAbsolute dir
-  projectPath <- canonicalizeConfigPath projectDir (ProjectConfigPath $ projectFileName :| [])
-  parseProjectSkeleton cacheDir httpTransport verbosity projectDir projectPath configToParse
+  projectPath@(ProjectConfigPath (canonicalRoot :| _)) <- canonicalizeConfigPath projectDir (ProjectConfigPath $ projectFileName :| [])
+  importsBy <- newIORef $ toNubList [(canonicalRoot, projectPath)]
+  parseProjectSkeleton cacheDir httpTransport verbosity importsBy projectDir projectPath configToParse
 
 parseProjectSkeleton
   :: FilePath
   -> HttpTransport
   -> Verbosity
+  -> IORef (NubList (FilePath, ProjectConfigPath))
+  -- ^ The imports seen so far, useful for reporting on duplicates and to detect duplicates that are not cycles
   -> FilePath
   -- ^ The directory of the project configuration, typically the directory of cabal.project
   -> ProjectConfigPath
@@ -258,7 +264,7 @@ parseProjectSkeleton
   -> ProjectConfigToParse
   -- ^ The contents of the file to parse
   -> IO (ParseResult ProjectConfigSkeleton)
-parseProjectSkeleton cacheDir httpTransport verbosity projectDir source (ProjectConfigToParse bs) =
+parseProjectSkeleton cacheDir httpTransport verbosity importsBy projectDir source (ProjectConfigToParse bs) =
   (sanityWalkPCS False =<<) <$> liftPR (go []) (ParseUtils.readFields bs)
   where
     go :: [ParseUtils.Field] -> [ParseUtils.Field] -> IO (ParseResult ProjectConfigSkeleton)
@@ -266,19 +272,26 @@ parseProjectSkeleton cacheDir httpTransport verbosity projectDir source (Project
       (ParseUtils.F _ "import" importLoc) -> do
         let importLocPath = importLoc `consProjectConfigPath` source
 
-        -- Once we canonicalize the import path, we can check for cyclical imports
-        normLocPath <- canonicalizeConfigPath projectDir importLocPath
+        -- Once we canonicalize the import path, we can check for cyclical and duplicate imports
+        normLocPath@(ProjectConfigPath (uniqueImport :| _)) <- canonicalizeConfigPath projectDir importLocPath
+        seenImportsBy@(fmap fst -> seenImports) <- fromNubList <$> atomicModifyIORef' importsBy (\ibs -> (toNubList [(uniqueImport, normLocPath)] <> ibs, ibs))
 
         debug verbosity $ "\nimport path, normalized\n=======================\n" ++ render (docProjectConfigPath normLocPath)
-
-        if isCyclicConfigPath normLocPath
-          then pure . parseFail $ ParseUtils.FromString (render $ cyclicalImportMsg normLocPath) Nothing
-          else do
-            normSource <- canonicalizeConfigPath projectDir source
-            let fs = (\z -> CondNode z [normLocPath] mempty) <$> fieldsToConfig normSource (reverse acc)
-            res <- parseProjectSkeleton cacheDir httpTransport verbosity projectDir importLocPath . ProjectConfigToParse =<< fetchImportConfig normLocPath
-            rest <- go [] xs
-            pure . fmap mconcat . sequence $ [fs, res, rest]
+        debug verbosity "\nseen unique paths\n================="
+        mapM_ (debug verbosity) seenImports
+        debug verbosity "\n"
+
+        if
+            | isCyclicConfigPath normLocPath ->
+                pure . parseFail $ ParseUtils.FromString (render $ cyclicalImportMsg normLocPath) Nothing
+            | uniqueImport `elem` seenImports -> do
+                pure . parseFail $ ParseUtils.FromString (render $ duplicateImportMsg uniqueImport normLocPath seenImportsBy) Nothing
+            | otherwise -> do
+                normSource <- canonicalizeConfigPath projectDir source
+                let fs = (\z -> CondNode z [normLocPath] mempty) <$> fieldsToConfig normSource (reverse acc)
+                res <- parseProjectSkeleton cacheDir httpTransport verbosity importsBy projectDir importLocPath . ProjectConfigToParse =<< fetchImportConfig normLocPath
+                rest <- go [] xs
+                pure . fmap mconcat . sequence $ [fs, res, rest]
       (ParseUtils.Section l "if" p xs') -> do
         subpcs <- go [] xs'
         let fs = singletonProjectConfigSkeleton <$> fieldsToConfig source (reverse acc)
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
index c2690ee4366..df9786ec44c 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
@@ -254,131 +254,17 @@ Could not resolve dependencies:
       (constraint from oops-0.project requires ==1.4.3.0)
 [__1] fail (backjumping, conflict set: hashable, oops)
 After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: hashable (3), oops (2)
-# checking if we detect when the same config is imported via many different paths (we don't)
+# checking that we detect when the same config is imported via many different paths
 # cabal v2-build
-Configuration is affected by the following files:
-- yops-0.project
-- yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-0.project
-- yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-0.project
-- yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-0.project
-- yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-0.project
-- yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-0.project
-- yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-0.project
-- yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops/yops-1.config
-    imported by: yops-0.project
-- yops/yops-3.config
-    imported by: yops-0.project
-- yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops/yops-5.config
-    imported by: yops-0.project
-- yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-0.project
-- yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops/yops-7.config
-    imported by: yops-0.project
-- yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-0.project
-- yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-0.project
-- yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
-    imported by: yops-2.config
-    imported by: yops/yops-1.config
-    imported by: yops-0.project
-- yops/yops-9.config
-    imported by: yops-0.project
-- yops/yops-9.config
-    imported by: yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-0.project
-- yops/yops-9.config
-    imported by: yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-0.project
-- yops/yops-9.config
-    imported by: yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
+Error: [Cabal-7090]
+Error parsing project file <ROOT>/yops-0.project:
+duplicate import of yops/yops-3.config;
+  yops/yops-3.config
     imported by: yops-0.project
-- yops/yops-9.config
-    imported by: yops-8.config
-    imported by: yops/yops-7.config
-    imported by: yops-6.config
-    imported by: yops/yops-5.config
-    imported by: yops-4.config
-    imported by: yops/yops-3.config
+  yops/yops-3.config
     imported by: yops-2.config
     imported by: yops/yops-1.config
     imported by: yops-0.project
-Up to date
 # checking bad conditional
 # cabal v2-build
 Error: [Cabal-7090]
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
index 67118d362c0..d404658ae93 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
@@ -252,11 +252,9 @@ main = cabalTest . withRepo "repo" . recordMode RecordMarked $ do
   --   +-- yops-8.config
   --    +-- yops/yops-9.config (no further imports)
   --  +-- yops/yops-9.config (no further imports)
-  --
-  -- We don't check and don't error or warn on the same config being imported
-  -- via many different paths.
-  log "checking if we detect when the same config is imported via many different paths (we don't)"
-  yopping <- cabal' "v2-build" [ "--project-file=yops-0.project" ]
+  log "checking that we detect when the same config is imported via many different paths"
+  yopping <- fails $ cabal' "v2-build" [ "--project-file=yops-0.project" ]
+  assertOutputContains (normalizeWindowsOutput "duplicate import of yops/yops-3.config") yopping
 
   log "checking bad conditional"
   badIf <- fails $ cabal' "v2-build" [ "--project-file=bad-conditional.project" ]
diff --git a/changelog.d/pr-9933 b/changelog.d/pr-9933
new file mode 100644
index 00000000000..d8a6c1d2337
--- /dev/null
+++ b/changelog.d/pr-9933
@@ -0,0 +1,23 @@
+synopsis: Detect non-cyclical duplicate project imports
+description:
+  Detect and report on duplicate imports that are non-cyclical and expand the
+  detail in cyclical import reporting, being more explicit and consistent with
+  non-cyclical duplicate reporting.
+
+  ```
+  $ cabal build --project-file=yops-0.project
+  ...
+  Error: [Cabal-7090]
+  Error parsing project file yops-0.project:
+  duplicate import of yops/yops-3.config;
+    yops/yops-3.config
+      imported by: yops-0.project
+    yops/yops-3.config
+      imported by: yops-2.config
+      imported by: yops/yops-1.config
+      imported by: yops-0.project
+  ```
+
+packages: cabal-install-solver cabal-install
+prs: #9578 #9933
+issues: #9562