diff --git a/src/Docs/Search/Declarations.purs b/src/Docs/Search/Declarations.purs
index 1535daf..403bfbb 100644
--- a/src/Docs/Search/Declarations.purs
+++ b/src/Docs/Search/Declarations.purs
@@ -1,6 +1,6 @@
 module Docs.Search.Declarations where
 
-import Docs.Search.DocsJson (ChildDeclType(..), ChildDeclaration(..), DeclType(..), Declaration(..), DocsJson(..))
+import Docs.Search.DocsJson (ChildDeclType(..), ChildDeclaration(..), DeclType(..), Declaration(..), DocsJson(..), SourceSpan)
 import Docs.Search.PackageIndex (Scores)
 import Docs.Search.SearchResult (ResultInfo(..), SearchResult(..))
 import Docs.Search.TypeDecoder (Constraint(..), QualifiedName(..), Type(..), Kind, joinForAlls)
@@ -87,7 +87,7 @@ resultsForDeclaration
 resultsForDeclaration scores moduleName indexEntry@(Declaration entry) =
   let { info, title, sourceSpan, comments, children } = entry
       { name, declLevel } = getLevelAndName info.declType title
-      packageName = extractPackageName sourceSpan.name
+      packageName = extractPackageName moduleName sourceSpan
   in case mkInfo declLevel indexEntry of
        Nothing -> mempty
        Just info' ->
@@ -95,7 +95,7 @@ resultsForDeclaration scores moduleName indexEntry@(Declaration entry) =
                                    , comments
                                    , hashAnchor: declLevelToHashAnchor declLevel
                                    , moduleName
-                                   , sourceSpan: Just sourceSpan
+                                   , sourceSpan
                                    , packageName
                                    , score: fromMaybe 0 $ Map.lookup packageName scores
                                    , info: info'
@@ -189,24 +189,22 @@ getLevelAndName DeclExternKind  name = { name, declLevel: KindLevel }
 
 
 -- | Extract package name from `sourceSpan.name`, which contains path to
--- | the source file.
-extractPackageName :: String -> String
-extractPackageName name =
-  let chunks = String.split (Pattern "/") name in
-  fromMaybe "<unknown>" $
-  chunks !! 0 >>= \dir ->
-  if dir == ".spago" then
-    chunks !! 1
-  else
-    let
-      bowerComponentsIndex =
-        Array.findIndex (_ == "bower_components") chunks
-    in
-      case bowerComponentsIndex of
-        Just n ->
-          chunks !! (n + 1)
-        Nothing ->
-          Just "<local package>"
+-- | the source file. If `ModuleName` string starts with `Prim.`, it's a
+-- | built-in (guaranteed by the compiler).
+extractPackageName :: ModuleName -> Maybe SourceSpan -> String
+extractPackageName moduleName _
+  | String.split (Pattern ".") moduleName !! 0 == Just "Prim" = "<builtin>"
+extractPackageName _ Nothing = "<unknown>"
+extractPackageName _ (Just { name }) =
+  let dirs = String.split (Pattern "/") name
+  in
+    fromMaybe "<local package>" do
+      topLevelDir <- dirs !! 0
+      if topLevelDir == ".spago"
+      then dirs !! 1
+      else do
+        bowerDirIx <- Array.findIndex (_ == "bower_components") dirs
+        dirs !! (bowerDirIx + 1)
 
 
 -- | Extract `SearchResults` from a `ChildDeclaration`.
diff --git a/src/Docs/Search/DocsJson.purs b/src/Docs/Search/DocsJson.purs
index c605eca..680d98a 100644
--- a/src/Docs/Search/DocsJson.purs
+++ b/src/Docs/Search/DocsJson.purs
@@ -33,6 +33,10 @@ instance decodeJsonDocsJson :: DecodeJson DocsJson where
 instance encodeJsonDocsJson :: EncodeJson DocsJson where
   encodeJson = encodeJson <<< unwrap
 
+type SourceSpan = { start :: Array Int
+                  , end :: Array Int
+                  , name :: String
+                  }
 
 newtype Declaration
   = Declaration { title :: String
@@ -46,10 +50,7 @@ newtype Declaration
                          , arguments     :: Maybe (Array TypeArgument)
                          , fundeps       :: Maybe FunDeps
                          }
-               , sourceSpan :: { start :: Array Int
-                               , end :: Array Int
-                               , name :: String
-                               }
+               , sourceSpan :: Maybe SourceSpan
                , children :: Array ChildDeclaration
                }
 
diff --git a/test/Main.purs b/test/Main.purs
index b38f824..ac2b506 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -5,6 +5,7 @@ import Prelude
 import Docs.Search.TypeDecoder (Constraint(..), FunDep(..), FunDeps(..), Kind(..), QualifiedName(..), Type(..))
 import Test.TypeQuery as TypeQuery
 import Test.IndexBuilder as IndexBuilder
+import Test.Declarations as Declarations
 
 import Test.Extra (assertRight)
 
@@ -26,6 +27,7 @@ mainTest :: TestSuite
 mainTest = do
   TypeQuery.tests
   IndexBuilder.tests
+  Declarations.tests
 
   let mkJson x = unsafePartial $ fromRight $ jsonParser x
   suite "FunDeps decoder" do
diff --git a/test/Test/Declarations.purs b/test/Test/Declarations.purs
new file mode 100644
index 0000000..fe3d9a3
--- /dev/null
+++ b/test/Test/Declarations.purs
@@ -0,0 +1,39 @@
+module Test.Declarations where
+
+import Prelude
+
+import Data.Maybe (Maybe(..))
+import Docs.Search.Declarations (extractPackageName)
+
+import Test.Unit (TestSuite, suite, test)
+import Test.Unit.Assert as Assert
+
+tests :: TestSuite
+tests = do
+  suite "Declarations" do
+    test "extractPackageName" do
+      Assert.equal "<builtin>" (extractPackageName "Prim" Nothing)
+      Assert.equal "<builtin>" (extractPackageName "Prim.Foo" Nothing)
+      Assert.equal "<builtin>" (extractPackageName "Prim.Foo.Bar" Nothing)
+      Assert.equal "<unknown>" (extractPackageName "Primitive" Nothing)
+      Assert.equal "foo"
+        (extractPackageName "Foo" $
+         Just { start: []
+              , end: []
+              , name: ".spago/foo/src/Foo.purs"
+              }
+        )
+      Assert.equal "bar"
+        (extractPackageName "Bar" $
+         Just { start: []
+              , end: []
+              , name: "/path/to/somewhere/bower_components/bar/src/Bar.purs"
+              }
+        )
+      Assert.equal "<local package>"
+        (extractPackageName "Bar" $
+         Just { start: []
+              , end: []
+              , name: "/path/to/somewhere/src/Bar.purs"
+              }
+        )