diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4e555e9..bd0e885 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,5 @@
 # v0.1.7
+- #21 Build scripts to exit on failure
 - #15 Mac OS X build of decode_barcodes
 - #14 Suffixes to resolve filename collisions
 
diff --git a/build.bat b/build.bat
index 60ae2a6..25ebdd3 100644
--- a/build.bat
+++ b/build.bat
@@ -2,10 +2,14 @@ REM Temporary solution until I get round to writing a makefile
 
 echo Clean
 del /S *pyc
-del *spec
 rmdir /Q /S dist build
 
+echo Check for presence of barcode engines
+python -c "from gouda.engines import ZbarEngine; assert ZbarEngine.available()" || exit /b
+python -c "from gouda.engines import LibDMTXEngine; assert LibDMTXEngine.available()" || exit /b
+python -c "from gouda.engines import InliteEngine; assert InliteEngine.available()" || exit /b
+
 echo Tests
-nosetests --with-coverage --cover-html --cover-inclusive --cover-erase --cover-tests --cover-package=gouda
+nosetests --with-coverage --cover-html --cover-inclusive --cover-erase --cover-tests --cover-package=gouda || exit /b
 
-pyinstaller --onefile --specpath=build gouda/scripts/decode_barcodes.py
+pyinstaller --onefile --clean decode_barcodes.spec || exit /b
diff --git a/build.sh b/build.sh
index e54c94d..8a91d66 100755
--- a/build.sh
+++ b/build.sh
@@ -7,6 +7,10 @@ find . -name "*pyc" -print0 | xargs -0 rm -rf
 find . -name __pycache__ -print0 | xargs -0 rm -rf
 rm -rf dist build cover
 
+echo Check for presence of barcode engines
+python -c "from gouda.engines import ZbarEngine; assert ZbarEngine.available()" || exit /b
+python -c "from gouda.engines import LibDMTXEngine; assert LibDMTXEngine.available()" || exit /b
+
 echo Tests
 nosetests --with-coverage --cover-html --cover-inclusive --cover-erase --cover-tests --cover-package=gouda
 
diff --git a/decode_barcodes.spec b/decode_barcodes.spec
index 867a8c4..339e9cf 100644
--- a/decode_barcodes.spec
+++ b/decode_barcodes.spec
@@ -18,38 +18,39 @@ a = Analysis(['gouda/scripts/decode_barcodes.py'],
              win_private_assemblies=False,
              cipher=block_cipher)
 
-# PyInstaller does not detect some dylibs, I think in some cases because they
-# are symlinked.
-# See Stack Overflow post http://stackoverflow.com/a/17595149 for example
-# of manipulating Analysis.binaries.
+if 'darwin' == sys.platform:
+    # PyInstaller does not detect some dylibs, I think in some cases because they
+    # are symlinked.
+    # See Stack Overflow post http://stackoverflow.com/a/17595149 for example
+    # of manipulating Analysis.binaries.
 
-MISSING_DYLIBS = (
-    'libpng16.16.dylib',
-    'libz.1.dylib',
-    'libopencv_contrib.2.4.dylib',
-    'libopencv_nonfree.2.4.dylib',
-    'libopencv_gpu.2.4.dylib',
-    'libopencv_legacy.2.4.dylib',
-    'libopencv_photo.2.4.dylib',
-    'libopencv_ocl.2.4.dylib',
-    'libopencv_calib3d.2.4.dylib',
-    'libopencv_features2d.2.4.dylib',
-    'libopencv_flann.2.4.dylib',
-    'libopencv_ml.2.4.dylib',
-    'libopencv_video.2.4.dylib',
-    'libopencv_objdetect.2.4.dylib',
-    'libopencv_highgui.2.4.dylib',
-    'libopencv_imgproc.2.4.dylib',
-    'libopencv_core.2.4.dylib',
-)
+    MISSING_DYLIBS = (
+        'libpng16.16.dylib',
+        'libz.1.dylib',
+        'libopencv_contrib.2.4.dylib',
+        'libopencv_nonfree.2.4.dylib',
+        'libopencv_gpu.2.4.dylib',
+        'libopencv_legacy.2.4.dylib',
+        'libopencv_photo.2.4.dylib',
+        'libopencv_ocl.2.4.dylib',
+        'libopencv_calib3d.2.4.dylib',
+        'libopencv_features2d.2.4.dylib',
+        'libopencv_flann.2.4.dylib',
+        'libopencv_ml.2.4.dylib',
+        'libopencv_video.2.4.dylib',
+        'libopencv_objdetect.2.4.dylib',
+        'libopencv_highgui.2.4.dylib',
+        'libopencv_imgproc.2.4.dylib',
+        'libopencv_core.2.4.dylib',
+    )
 
-# The lib directory associated with this environment
-LIB = Path(sys.argv[0]).parent.parent.joinpath('lib')
+    # The lib directory associated with this environment
+    LIB = Path(sys.argv[0]).parent.parent.joinpath('lib')
 
-# Find the source for each library and add it to the list of binaries
-a.binaries += TOC([
-    (lib, str(LIB.joinpath(lib).resolve()), 'BINARY') for lib in MISSING_DYLIBS
-])
+    # Find the source for each library and add it to the list of binaries
+    a.binaries += TOC([
+        (lib, str(LIB.joinpath(lib).resolve()), 'BINARY') for lib in MISSING_DYLIBS
+    ])
 
 pyz = PYZ(a.pure, a.zipped_data,
              cipher=block_cipher)
diff --git a/gouda/tests/test_decode_barcodes.py b/gouda/tests/test_decode_barcodes.py
index 8d02c16..20794b8 100644
--- a/gouda/tests/test_decode_barcodes.py
+++ b/gouda/tests/test_decode_barcodes.py
@@ -48,7 +48,7 @@ def test_rename_with_collisions(self):
             main(['zbar', '--action=rename', unicode(tempdir)])
             self.assertEqual(
                 ['Stegosaurus.png', 'first copy.png', 'second copy.png'],
-                [path.name for path in sorted(tempdir.iterdir())]
+                [path.name for path in sorted(tempdir.iterdir(), key=lambda p: p.name)]
             )
 
     def test_rename_avoid_collisions(self):