diff --git a/trunk/PKGBUILD b/trunk/PKGBUILD
index d2bb05f..eedfd16 100644
--- a/trunk/PKGBUILD
+++ b/trunk/PKGBUILD
@@ -24,9 +24,9 @@ b2sums=('e208c6632782eeef97e9aa9d7fb3320d7625f416de04640d9ae86ce6d66ee5ad0a7c8d7
         'SKIP'
         'a42039f8419417a312ccdb65a01b22c5e1133ebaa3e3a905387565bf2e3991ce3efb74f3b2fb0ec5e8408b665044946337c6ecfd4af1083ae2811aad9dc7d76e')
 validpgpkeys=('0B3972B2D9E32EAB423D2E0F22BE0C62FFBFA548') # Thomas Nagy <tnagy@waf.io>
-_py_ver=$(python3 -c "import sys; print(str(sys.version_info.major)+'.'+str(sys.version_info.minor))")
 
 prepare() {
+  local _py_ver=$(python3 -c "import sys; print(str(sys.version_info.major)+'.'+str(sys.version_info.minor))")
   cd $pkgname-$pkgver
   # make waf find its waflib
   sed -e "/test(i/ s|dirname|'python${_py_ver}/site-packages/waf'|" -i waf-light
@@ -46,6 +46,7 @@ build() {
 }
 
 package() {
+  local _py_ver=$(python3 -c "import sys; print(str(sys.version_info.major)+'.'+str(sys.version_info.minor))")
   cd $pkgname-$pkgver
   install -vDm 755 waf -t "$pkgdir/usr/bin"
   install -vDm 644 wscript -t "$pkgdir/usr/share/$pkgname/"