diff --git a/build.sh b/build.sh
index 32cc3ea..450e231 100644
--- a/build.sh
+++ b/build.sh
@@ -10,8 +10,9 @@ pkgver=85.0.2
 
 fetch() {
     # fetch the firefox source.
-    rm -vf firefox-$pkgver.source.tar.xz
+    rm -f firefox-$pkgver.source.tar.xz
     wget https://archive.mozilla.org/pub/firefox/releases/$pkgver/source/firefox-$pkgver.source.tar.xz
+    if [ ! -f firefox-$pkgver.source.tar.xz ]; then exit 1; fi
     
     # the settings and common submodules should be checked out with --recursive to allow the build
     
@@ -19,8 +20,11 @@ fetch() {
     echo 'Getting patches..'
     rm -f megabar.patch remove_addons.patch unity-menubar.patch
     wget -q https://gitlab.com/librewolf-community/browser/linux/-/raw/master/megabar.patch
+    if [ ! -f megabar.patch ]; then exit 1; fi
     wget -q https://gitlab.com/librewolf-community/browser/linux/-/raw/master/remove_addons.patch
+    if [ ! -f remove_addons.patch ]; then exit 1; fi
     wget -q https://gitlab.com/librewolf-community/browser/linux/-/raw/master/unity-menubar.patch
+    if [ ! -f unity-menubar.patch ]; then exit 1; fi
 }
 
 
@@ -31,6 +35,7 @@ prepare() {
     echo "Extracting firefox-$pkgver.source.tar.xz ..."
     tar xf firefox-$pkgver.source.tar.xz
 
+    if [ ! -d firefox-$pkgver ]; then exit 1; fi
     cd firefox-$pkgver
     
     cat >../mozconfig <<END
@@ -133,22 +138,27 @@ END
 
 
 build() {
+    if [ ! -d firefox-$pkgver ]; then exit 1; fi
     cd firefox-$pkgver
     ./mach build
+    if [ $? -ne 0 ]; then exit 1; fi
     cd ..
 }
 
 
 
 package() {
+    if [ ! -d firefox-$pkgver ]; then exit 1; fi
     cd firefox-$pkgver
     ./mach package
+    if [ $? -ne 0 ]; then exit 1; fi
     cd ..
 }
 
 
 
 installer_win() {
+    if [ ! -d firefox-$pkgver ]; then exit 1; fi
     cd firefox-$pkgver
 
     # there is just too much garbage in this installer function to
diff --git a/installer_win.sh b/installer_win.sh
index bd9110f..6e9908c 100644
--- a/installer_win.sh
+++ b/installer_win.sh
@@ -1,3 +1,6 @@
+# sanity checks
+if [ ! -d obj-x86_64-pc-mingw32/dist ]; then exit 1; fi
+
 # apply the LibreWolf settings
 cp -rv ../settings/* obj-x86_64-pc-mingw32/dist/librewolf
     
@@ -8,7 +11,9 @@ cd obj-x86_64-pc-mingw32/dist
  # be sure to remove the previous zip file..
  rm -vf librewolf-$pkgver.en-US.win64.txt librewolf-$pkgver.en-US.win64.zip
  zip -r9 librewolf-$pkgver.en-US.win64.zip librewolf
- /c/mozilla-source/Git/usr/bin/sha256sum.exe librewolf-$pkgver.en-US.win64.zip > librewolf-$pkgver.en-US.win64.zip.sha256sum
+ if [ $? -ne 0 ]; then exit 1; fi
+ sha256sum.exe librewolf-$pkgver.en-US.win64.zip > librewolf-$pkgver.en-US.win64.zip.sha256sum
+ if [ $? -ne 0 ]; then exit 1; fi
  # copy the resulting zip file
  rm -vf ../../../librewolf-$pkgver.en-US.win64.zip*
  cp -v librewolf-$pkgver.en-US.win64.zip* ../../..
@@ -111,7 +116,10 @@ END
 pushd ..
  rm -vrf librewolf
  unzip librewolf-$pkgver.en-US.win64.zip
+ if [ $? -ne 0 ]; then exit 1; fi
  cp -v common/source_files/browser/branding/librewolf/firefox.ico librewolf/librewolf.ico
  makensis-3.01.exe installer_win.nsi
- /c/mozilla-source/Git/usr/bin/sha256sum.exe librewolf-$pkgver.en-US.win64-setup.exe > librewolf-$pkgver.en-US.win64-setup.exe.sha256sum
+ if [ $? -ne 0 ]; then exit 1; fi
+ sha256sum.exe librewolf-$pkgver.en-US.win64-setup.exe > librewolf-$pkgver.en-US.win64-setup.exe.sha256sum
+ if [ $? -ne 0 ]; then exit 1; fi
 popd