diff --git a/ringo/src/Ringo/Extractor/Internal.hs b/ringo/src/Ringo/Extractor/Internal.hs
index c301efc..5486a9f 100644
--- a/ringo/src/Ringo/Extractor/Internal.hs
+++ b/ringo/src/Ringo/Extractor/Internal.hs
@@ -35,6 +35,18 @@ dimColumnName :: Text -> ColumnName -> ColumnName
 dimColumnName dimName columnName =
   fromMaybe columnName . Text.stripPrefix (dimName <> "_") $ columnName
 
+dimColumnMapping :: Text -> Fact -> TableName -> [(ColumnName, ColumnName)]
+dimColumnMapping dimPrefix fact dimTableName =
+  [ (dimColumnName factColTargetTable factColTargetColumn, factColTargetColumn)
+    | FactColumn { factColType = DimVal {..}, ..} <- factColumns fact
+    , dimPrefix <> factColTargetTable == dimTableName ]
+
+dimColumnMappings :: Text -> Fact -> [(TableName, [(ColumnName, ColumnName)])]
+dimColumnMappings dimPrefix fact =
+  nub [ (dimTableName, dimColumnMapping dimPrefix fact dimTableName)
+        | FactColumn { factColType = DimVal {..}, ..} <- factColumns fact
+        , let dimTableName = dimPrefix <> factColTargetTable ]
+
 timeUnitColumnName :: Text -> ColumnName -> TimeUnit -> ColumnName
 timeUnitColumnName dimIdColName colName timeUnit =
   colName <> "_" <> timeUnitName timeUnit <> "_" <> dimIdColName
diff --git a/ringo/src/Ringo/Generator/Internal.hs b/ringo/src/Ringo/Generator/Internal.hs
index f1fdbcf..08fa4dd 100644
--- a/ringo/src/Ringo/Generator/Internal.hs
+++ b/ringo/src/Ringo/Generator/Internal.hs
@@ -7,7 +7,7 @@ import qualified Data.Map as Map
 import qualified Data.Text as Text
 
 import Database.HsSqlPpp.Syntax (ScalarExpr)
-import Data.List                (find)
+import Data.List                (find, nub)
 import Data.Monoid              ((<>))
 import Data.Text                (Text)
 
@@ -15,12 +15,6 @@ import Ringo.Extractor.Internal
 import Ringo.Generator.Sql
 import Ringo.Types
 
-dimColumnMapping :: Text -> Fact -> TableName -> [(ColumnName, ColumnName)]
-dimColumnMapping dimPrefix fact dimTableName =
-  [ (dimColumnName factColTargetTable factColTargetColumn, factColTargetColumn)
-    | FactColumn { factColType = DimVal {..}, ..} <- factColumns fact
-    , dimPrefix <> factColTargetTable == dimTableName ]
-
 coalesceColumn :: TypeDefaults -> TableName -> Column -> ScalarExpr
 coalesceColumn defaults tName Column{..} =
   if columnNullable == Null
diff --git a/ringo/src/Ringo/Types.hs b/ringo/src/Ringo/Types.hs
index 4b2b56e..8eecd97 100644
--- a/ringo/src/Ringo/Types.hs
+++ b/ringo/src/Ringo/Types.hs
@@ -3,13 +3,32 @@
 {-# LANGUAGE Rank2Types #-}
 
 module Ringo.Types
-  ( ColumnName, ColumnType, TableName
-  , Nullable(..), Column(..), TableConstraint(..), Table(..)
-  , TimeUnit(..), timeUnitName, timeUnitToSeconds
-  , Fact(..), FactColumnType(..), FactColumn(..), factSourceColumnName
-  , Settings(..), defSettings
-  , ValidationError(..), TypeDefaults
-  , Env, envTables, envFacts, envSettings, envTypeDefaults,
-  TablePopulationMode(..), Dependencies) where
+  ( ColumnName
+  , ColumnType
+  , TableName
+  , Nullable(..)
+  , Column(..)
+  , TableConstraint(..)
+  , Table(..)
+  , TimeUnit(..)
+  , timeUnitName
+  , timeUnitToSeconds
+  , Fact(..)
+  , FactColumnKind(..)
+  , FactColumnType(..)
+  , FactColumn(..)
+  , factSourceColumnName
+  , Settings(..)
+  , defSettings
+  , ValidationError(..)
+  , TypeDefaults
+  , Env
+  , envTables
+  , envFacts
+  , envSettings
+  , envTypeDefaults
+  , TablePopulationMode(..)
+  , Dependencies
+  ) where
 
 import Ringo.Types.Internal
diff --git a/ringo/src/Ringo/Types/Internal.hs b/ringo/src/Ringo/Types/Internal.hs
index 6c6bbbe..ebffbfc 100644
--- a/ringo/src/Ringo/Types/Internal.hs
+++ b/ringo/src/Ringo/Types/Internal.hs
@@ -161,6 +161,7 @@ data ValidationError = MissingTable             !TableName
                      | MissingColumn            !TableName !ColumnName
                      | DuplicateColumn          !TableName !ColumnName
                      | MissingTimeColumn        !TableName
+                     | DuplicateDimension       !TableName
                      | MissingNotNullConstraint !TableName !ColumnName
                      | MissingTypeDefault       !Text
                      deriving (Eq, Show)
diff --git a/ringo/src/Ringo/Validator.hs b/ringo/src/Ringo/Validator.hs
index 547e98c..e773f3f 100644
--- a/ringo/src/Ringo/Validator.hs
+++ b/ringo/src/Ringo/Validator.hs
@@ -15,8 +15,9 @@ import Control.Applicative ((<$>))
 #endif
 
 import Control.Monad.Reader (Reader, ask, runReader)
+import Data.Function        (on)
 import Data.Maybe           (isJust, fromJust)
-import Data.List            (nub, group, sort)
+import Data.List            (nub, group, groupBy, sort)
 
 import Ringo.Extractor.Internal
 import Ringo.Types
@@ -92,7 +93,7 @@ validateFact Fact {..} = do
       _                                  -> []
 
 validateEnv :: [Table] -> [Fact] -> Settings -> TypeDefaults -> Either [ValidationError] Env
-validateEnv tables facts settings typeDefaults =
+validateEnv tables facts settings@Settings {..} typeDefaults =
   flip runReader (RawEnv tables facts settings typeDefaults) $ do
     tableVs <- concat <$> mapM validateTable tables
     factVs  <- concat <$> mapM validateFact facts
@@ -101,7 +102,13 @@ validateEnv tables facts settings typeDefaults =
     let dupColVs   = [ DuplicateColumn tableName col
                        | Table{..} <- tables
                        , col       <- findDups . map columnName $ tableColumns ]
-    let vs = nub $ tableVs ++ factVs ++ dupTableVs ++ dupFactVs ++ dupColVs
+    let dupDimVs   = facts
+                     >>- concatMap (dimColumnMappings settingDimPrefix)
+                     >>> sort
+                     >>> groupBy ((==) `on` fst)
+                     >>> filter (map snd >>> nub >>> length >>> (/= 1))
+                     >>> map (head >>> fst >>> DuplicateDimension)
+        vs = nub $ tableVs ++ factVs ++ dupTableVs ++ dupFactVs ++ dupColVs ++ dupDimVs
     if null vs
       then return . Right $ Env tables facts settings typeDefaults
       else return . Left  $ vs