diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+1.0.17
+
+* [Handle `.drv` and `.nix` files that contain non-UTF8 text](https://github.com/Gabriel439/nix-diff/pull/50)
+
 1.0.16
 
 * [Accept realised store paths as input](https://github.com/Gabriel439/nix-diff/pull/47)
diff --git a/nix-diff.cabal b/nix-diff.cabal
--- a/nix-diff.cabal
+++ b/nix-diff.cabal
@@ -1,5 +1,5 @@
 name:                nix-diff
-version:             1.0.16
+version:             1.0.17
 synopsis:            Explain why two Nix derivations differ
 description:         This package provides a @nix-diff@ executable which
                      explains why two Nix derivations (i.e. @*.drv@ files)
@@ -21,6 +21,7 @@
   main-is:             Main.hs
   build-depends:       base                 >= 4.9      && < 5
                      , attoparsec           >= 0.13     && < 0.14
+                     , bytestring           >= 0.9      && < 0.12
                      , containers           >= 0.5      && < 0.7
                      , directory                           < 1.4
                      , mtl                  >= 2.2      && < 2.3
diff --git a/src/Main.hs b/src/Main.hs
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -49,6 +49,9 @@
 
 #if MIN_VERSION_base(4,9,0)
 import Control.Monad.Fail (MonadFail)
+import qualified Data.ByteString
+import qualified Data.Text.Encoding
+import qualified Data.Text.Encoding.Error
 #endif
 
 data Color = Always | Auto | Never
@@ -208,11 +211,20 @@
       where
         predicate key' = buildProductName key == buildProductName key'
 
+-- | Read a file as utf-8 encoded string, replacing non-utf-8 characters
+-- with the unicode replacement character.
+-- This is necessary since derivations (and nix source code!) can in principle
+-- contain arbitrary bytes, but `nix-derivation` can only parse from 'Text'.
+readFileUtf8Lenient :: FilePath -> IO Text
+readFileUtf8Lenient file =
+    Data.Text.Encoding.decodeUtf8With Data.Text.Encoding.Error.lenientDecode
+        <$> Data.ByteString.readFile file
+
 -- | Read and parse a derivation from a file
 readDerivation :: FilePath -> Diff (Derivation FilePath Text)
 readDerivation path = do
     let string = path
-    text <- liftIO (Text.IO.readFile string)
+    text <- liftIO (readFileUtf8Lenient string)
     case Data.Attoparsec.Text.parse Nix.Derivation.parseDerivation text of
         Done _ derivation -> do
             return derivation
@@ -573,8 +585,8 @@
                 rightExists <- liftIO (Directory.doesFileExist rightPath)
                 if leftExists && rightExists
                     then do
-                        leftText  <- liftIO (Text.IO.readFile leftPath)
-                        rightText <- liftIO (Text.IO.readFile rightPath)
+                        leftText  <- liftIO (readFileUtf8Lenient leftPath)
+                        rightText <- liftIO (readFileUtf8Lenient rightPath)
 
                         text <- diffText leftText rightText
                         echo ("    " <> text)