diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # citeproc changelog
 
+## 0.3
+
+  * Change `makeReferenceMap` to return a cleaned-up list of
+    references as well as a reference map.  The cleanup-up list
+    removes references with duplicate ids.  When there are multiple
+    references with the same id, the last one is included and
+    the others discarded.  [API change]
+
 ## 0.2.0.1
 
   * FromJSON for Name: make straight quotes curly.
diff --git a/citeproc.cabal b/citeproc.cabal
--- a/citeproc.cabal
+++ b/citeproc.cabal
@@ -1,6 +1,6 @@
 cabal-version:       2.2
 name:                citeproc
-version:             0.2.0.1
+version:             0.3
 synopsis:            Generates citations and bibliography from CSL styles.
 description:         citeproc parses CSL style files and uses them to
                      generate a list of formatted citations and bibliography
diff --git a/man/citeproc.1 b/man/citeproc.1
--- a/man/citeproc.1
+++ b/man/citeproc.1
@@ -1,6 +1,6 @@
-.\" Automatically generated by Pandoc 2.11.2
+.\" Automatically generated by Pandoc 2.11.3
 .\"
-.TH "citeproc" "1" "" "citeproc 0.2.0.1" ""
+.TH "citeproc" "1" "" "citeproc 0.3" ""
 .hy
 .SH NAME
 .PP
diff --git a/src/Citeproc/Eval.hs b/src/Citeproc/Eval.hs
--- a/src/Citeproc/Eval.hs
+++ b/src/Citeproc/Eval.hs
@@ -86,9 +86,11 @@
            -> [Citation a]     -- ^ List of citations.
            -> ([Output a], [(Text, Output a)], [Text])
                        -- ^ (citations, (id, bibentry) pairs, warnings)
-evalStyle style mblang refs citations =
+evalStyle style mblang refs' citations =
   (citationOs, bibliographyOs, Set.toList warnings)
  where
+  (refs, refmap) = makeReferenceMap refs'
+
   ((citationOs, bibliographyOs), warnings) = evalRWS go
      Context
       { contextLocale              = mergeLocales mblang style
@@ -105,7 +107,7 @@
       { stateVarCount = VarCount 0 0
       , stateLastCitedMap = mempty
       , stateNoteMap = mempty
-      , stateRefMap = makeReferenceMap refs
+      , stateRefMap = refmap
       , stateReference = Reference mempty mempty Nothing mempty
       , stateUsedYearSuffix = False
       }
diff --git a/src/Citeproc/Types.hs b/src/Citeproc/Types.hs
--- a/src/Citeproc/Types.hs
+++ b/src/Citeproc/Types.hs
@@ -103,6 +103,7 @@
   , Inputs(..)
   )
 where
+import qualified Data.Set as Set
 import qualified Data.Map as M
 import qualified Data.Text.Read as TR
 import qualified Data.Scientific as S
@@ -1061,9 +1062,20 @@
   ReferenceMap { unReferenceMap :: M.Map ItemId (Reference a) }
   deriving (Show)
 
-makeReferenceMap :: [Reference a] -> ReferenceMap a
-makeReferenceMap refs =
-  ReferenceMap (M.fromList (map (\r -> (referenceId r, r)) refs))
+-- | Returns a pair consisting of the cleaned up list of
+-- references and a reference map.  If the original reference
+-- list contains items with the same id, then the one that
+-- occurs last in the list is retained, and the others are
+-- omittedfrom the cleaned-up list.
+makeReferenceMap :: [Reference a] -> ([Reference a], ReferenceMap a)
+makeReferenceMap = snd . foldr go (mempty, ([], ReferenceMap mempty))
+  where
+   go ref (ids, (rs, ReferenceMap refmap)) =
+     let rid = referenceId ref
+      in if Set.member rid ids
+            then (ids, (rs, ReferenceMap refmap))
+            else (Set.insert rid ids,
+                   (ref:rs, ReferenceMap (M.insert rid ref refmap)))
 
 lookupReference :: ItemId -> ReferenceMap a -> Maybe (Reference a)
 lookupReference ident (ReferenceMap m) = M.lookup ident m