diff --git a/appveyor.yml b/appveyor.yml
index 1389bebe..e108412d 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -14,8 +14,8 @@ install:
 build_script:
 - cmd: >-
     cd \projects\yggdrasil-go
-- c:\msys64\usr\bin\bash -lc "./contrib/msi/build-msi.sh x64"
-- c:\msys64\usr\bin\bash -lc "./contrib/msi/build-msi.sh x86"
+    c:\msys64\usr\bin\bash -lc "./contrib/msi/build-msi.sh x64"
+    c:\msys64\usr\bin\bash -lc "./contrib/msi/build-msi.sh x86"
 
 test: off
 
diff --git a/contrib/msi/build-msi.sh b/contrib/msi/build-msi.sh
index 3346c069..c357dbf9 100644
--- a/contrib/msi/build-msi.sh
+++ b/contrib/msi/build-msi.sh
@@ -36,8 +36,10 @@ then
 fi
 
 # Check the prerequisite files are in place
-[ "${PKGARCH}" == "x64" ] && GOARCH=amd64 CGO_ENABLED=0 ./build || \
-[ "${PKGARCH}" == "x86" ] && GOARCH=386 CGO_ENABLED=0 ./build || \
+(
+  [ "${PKGARCH}" == "x64" ] && GOOS=windows GOARCH=amd64 CGO_ENABLED=0 ./build
+  [ "${PKGARCH}" == "x86" ] && GOOS=windows GOARCH=386 CGO_ENABLED=0 ./build
+) || \
 (
   echo "failed to build Yggdrasil"
   exit 1