diff --git a/src/Data/Text/Internal/Builder.hs b/src/Data/Text/Internal/Builder.hs
index 66858251..db27bfe1 100644
--- a/src/Data/Text/Internal/Builder.hs
+++ b/src/Data/Text/Internal/Builder.hs
@@ -62,7 +62,7 @@ import Data.Monoid (Monoid(..))
 #if !MIN_VERSION_base(4,11,0) && MIN_VERSION_base(4,9,0)
 import Data.Semigroup (Semigroup(..))
 #endif
-import Data.Text.Internal (Text(..))
+import Data.Text.Internal (Text(..), safe)
 import Data.Text.Internal.Lazy (smallChunkSize)
 import Data.Text.Unsafe (inlineInterleaveST)
 import Data.Text.Internal.Unsafe.Char (unsafeWrite)
@@ -138,7 +138,7 @@ empty = Builder (\ k buf -> k buf)
 --  * @'toLazyText' ('singleton' c) = 'L.singleton' c@
 --
 singleton :: Char -> Builder
-singleton c = writeAtMost 2 $ \ marr o -> unsafeWrite marr o c
+singleton c = writeAtMost 2 $ \ marr o -> unsafeWrite marr o (safe c)
 {-# INLINE singleton #-}
 
 ------------------------------------------------------------------------
@@ -190,7 +190,7 @@ fromString str = Builder $ \k (Buffer p0 o0 u0 l0) ->
                 ts <- inlineInterleaveST (loop marr' 0 0 chunkSize s)
                 return $ t : ts
             | otherwise = do
-                n <- unsafeWrite marr (o+u) c
+                n <- unsafeWrite marr (o+u) (safe c)
                 loop marr o (u+n) (l-n) cs
     in loop p0 o0 u0 l0 str
   where
diff --git a/tests/Tests/Regressions.hs b/tests/Tests/Regressions.hs
index 4d236d19..ed023f27 100644
--- a/tests/Tests/Regressions.hs
+++ b/tests/Tests/Regressions.hs
@@ -23,6 +23,7 @@ import qualified Data.Text.Encoding as TE
 import qualified Data.Text.Internal as T
 import qualified Data.Text.IO as T
 import qualified Data.Text.Lazy as LT
+import qualified Data.Text.Lazy.Builder as TB
 import qualified Data.Text.Lazy.Encoding as LE
 import qualified Data.Text.Unsafe as T
 import qualified Test.Tasty as F
@@ -101,6 +102,18 @@ t227 =
                 (T.length $ T.filter isLetter $ T.take (-3) "Hello! How are you doing today?")
                 0
 
+t280_fromString :: IO ()
+t280_fromString =
+    assertEqual "TB.fromString performs replacement on invalid scalar values"
+                (TB.toLazyText (TB.fromString "\xD800"))
+                (LT.pack "\xFFFD")
+
+t280_singleton :: IO ()
+t280_singleton =
+    assertEqual "TB.singleton performs replacement on invalid scalar values"
+                (TB.toLazyText (TB.singleton '\xD800'))
+                (LT.pack "\xFFFD")
+
 -- See GitHub issue #301
 -- This tests whether the "TEXT take . drop -> unfused" rule is applied to the
 -- slice function. When the slice function is fused, a new array will be
@@ -129,5 +142,7 @@ tests = F.testGroup "Regressions"
     , F.testCase "t197" t197
     , F.testCase "t221" t221
     , F.testCase "t227" t227
+    , F.testCase "t280/fromString" t280_fromString
+    , F.testCase "t280/singleton" t280_singleton
     , F.testCase "t301" t301
     ]