diff --git a/pkgs/development/libraries/qt-5/hooks/qtbase-setup-hook.sh b/pkgs/development/libraries/qt-5/hooks/qtbase-setup-hook.sh
index 436c2e1d032a..836e154148be 100644
--- a/pkgs/development/libraries/qt-5/hooks/qtbase-setup-hook.sh
+++ b/pkgs/development/libraries/qt-5/hooks/qtbase-setup-hook.sh
@@ -61,6 +61,6 @@ postPatchMkspecs() {
         fixQtBuiltinPaths "$dev/mkspecs" '*.pr?'
     fi
 }
-if [ -z "$dontPatchMkspecs" ]; then
+if [ -z "${dontPatchMkspecs-}" ]; then
     postPhases="${postPhases}${postPhases:+ }postPatchMkspecs"
 fi
diff --git a/pkgs/development/tools/build-managers/cmake/setup-hook.sh b/pkgs/development/tools/build-managers/cmake/setup-hook.sh
index b8716c5251eb..dbd40bf71242 100755
--- a/pkgs/development/tools/build-managers/cmake/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/cmake/setup-hook.sh
@@ -20,17 +20,17 @@ cmakeConfigurePhase() {
         export CTEST_PARALLEL_LEVEL=$NIX_BUILD_CORES
     fi
 
-    if [ -z "$dontFixCmake" ]; then
+    if [ -z "${dontFixCmake-}" ]; then
         fixCmakeFiles .
     fi
 
-    if [ -z "$dontUseCmakeBuildDir" ]; then
+    if [ -z "${dontUseCmakeBuildDir-}" ]; then
         mkdir -p build
         cd build
         cmakeDir=${cmakeDir:-..}
     fi
 
-    if [ -z "$dontAddPrefix" ]; then
+    if [ -z "${dontAddPrefix-}" ]; then
         cmakeFlags="-DCMAKE_INSTALL_PREFIX=$prefix $cmakeFlags"
     fi
 
@@ -84,7 +84,7 @@ cmakeConfigurePhase() {
     cmakeFlags="-DCMAKE_INSTALL_LOCALEDIR=${!outputLib}/share/locale $cmakeFlags"
 
     # Don’t build tests when doCheck = false
-    if [ -z "$doCheck" ]; then
+    if [ -z "${doCheck-}" ]; then
         cmakeFlags="-DBUILD_TESTING=OFF $cmakeFlags"
     fi
 
@@ -115,7 +115,7 @@ cmakeConfigurePhase() {
     runHook postConfigure
 }
 
-if [ -z "$dontUseCmakeConfigure" -a -z "$configurePhase" ]; then
+if [ -z "${dontUseCmakeConfigure-}" -a -z "$configurePhase" ]; then
     setOutputFlags=
     configurePhase=cmakeConfigurePhase
 fi
diff --git a/pkgs/development/tools/build-managers/gn/setup-hook.sh b/pkgs/development/tools/build-managers/gn/setup-hook.sh
index 75d2edcaf1c6..4f772d2369ba 100644
--- a/pkgs/development/tools/build-managers/gn/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/gn/setup-hook.sh
@@ -9,6 +9,6 @@ gnConfigurePhase() {
     runHook postConfigure
 }
 
-if [ -z "$dontUseGnConfigure" -a -z "$configurePhase" ]; then
+if [ -z "${dontUseGnConfigure-}" -a -z "$configurePhase" ]; then
     configurePhase=gnConfigurePhase
 fi
diff --git a/pkgs/development/tools/build-managers/meson/setup-hook.sh b/pkgs/development/tools/build-managers/meson/setup-hook.sh
index 6e8d94523e14..bfb40303cd85 100644
--- a/pkgs/development/tools/build-managers/meson/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/meson/setup-hook.sh
@@ -1,7 +1,7 @@
 mesonConfigurePhase() {
     runHook preConfigure
 
-    if [ -z "$dontAddPrefix" ]; then
+    if [ -z "${dontAddPrefix-}" ]; then
         mesonFlags="--prefix=$prefix $mesonFlags"
     fi
 
@@ -36,7 +36,7 @@ mesonConfigurePhase() {
     runHook postConfigure
 }
 
-if [ -z "$dontUseMesonConfigure" -a -z "$configurePhase" ]; then
+if [ -z "${dontUseMesonConfigure-}" -a -z "$configurePhase" ]; then
     setOutputFlags=
     configurePhase=mesonConfigurePhase
 fi
diff --git a/pkgs/development/tools/build-managers/ninja/setup-hook.sh b/pkgs/development/tools/build-managers/ninja/setup-hook.sh
index e3c67bd139dd..76de25aaabf1 100644
--- a/pkgs/development/tools/build-managers/ninja/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/ninja/setup-hook.sh
@@ -19,7 +19,7 @@ ninjaBuildPhase() {
     runHook postBuild
 }
 
-if [ -z "$dontUseNinjaBuild" -a -z "$buildPhase" ]; then
+if [ -z "${dontUseNinjaBuild-}" -a -z "$buildPhase" ]; then
     buildPhase=ninjaBuildPhase
 fi
 
@@ -38,7 +38,7 @@ ninjaInstallPhase() {
     runHook postInstall
 }
 
-if [ -z "$dontUseNinjaInstall" -a -z "$installPhase" ]; then
+if [ -z "${dontUseNinjaInstall-}" -a -z "$installPhase" ]; then
     installPhase=ninjaInstallPhase
 fi
 
@@ -73,6 +73,6 @@ ninjaCheckPhase() {
     runHook postCheck
 }
 
-if [ -z "$dontUseNinjaCheck" -a -z "$checkPhase" ]; then
+if [ -z "${dontUseNinjaCheck-}" -a -z "$checkPhase" ]; then
     checkPhase=ninjaCheckPhase
 fi
diff --git a/pkgs/development/tools/build-managers/scons/setup-hook.sh b/pkgs/development/tools/build-managers/scons/setup-hook.sh
index 55159aa5a93a..428852ac574a 100644
--- a/pkgs/development/tools/build-managers/scons/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/scons/setup-hook.sh
@@ -75,7 +75,7 @@ if [ -z "$buildPhase" ]; then
     buildPhase=sconsBuildPhase
 fi
 
-if [ -z "$dontUseSconsInstall" -a -z "$installPhase" ]; then
+if [ -z "${dontUseSconsInstall-}" -a -z "$installPhase" ]; then
     installPhase=sconsInstallPhase
 fi
 
diff --git a/pkgs/servers/x11/xorg/imake-setup-hook.sh b/pkgs/servers/x11/xorg/imake-setup-hook.sh
index 10f54198f7fb..e743093af0ec 100644
--- a/pkgs/servers/x11/xorg/imake-setup-hook.sh
+++ b/pkgs/servers/x11/xorg/imake-setup-hook.sh
@@ -14,6 +14,6 @@ imakeConfigurePhase() {
     runHook postConfigure
 }
 
-if [ -z "$dontUseImakeConfigure" -a -z "$configurePhase" ]; then
+if [ -z "${dontUseImakeConfigure-}" -a -z "$configurePhase" ]; then
     configurePhase=imakeConfigurePhase
 fi