diff --git a/pkgs/build-support/setup-hooks/multiple-outputs.sh b/pkgs/build-support/setup-hooks/multiple-outputs.sh
index 8a62c57dbd07..45096d833b42 100644
--- a/pkgs/build-support/setup-hooks/multiple-outputs.sh
+++ b/pkgs/build-support/setup-hooks/multiple-outputs.sh
@@ -69,8 +69,8 @@ _multioutConfig() {
     # try to detect share/doc/${shareDocName}
     # Note: sadly, $configureScript detection comes later in configurePhase,
     #   and reordering would cause more trouble than worth.
-    if [ -z "$shareDocName" ]; then
-        local confScript="$configureScript"
+    if [ -z "${shareDocName:-}" ]; then
+        local confScript="${configureScript:-}"
         if [ -z "$confScript" ] && [ -x ./configure ]; then
             confScript=./configure
         fi
diff --git a/pkgs/build-support/setup-hooks/patch-shebangs.sh b/pkgs/build-support/setup-hooks/patch-shebangs.sh
index e6872db1acd7..a22f989362c4 100644
--- a/pkgs/build-support/setup-hooks/patch-shebangs.sh
+++ b/pkgs/build-support/setup-hooks/patch-shebangs.sh
@@ -75,7 +75,7 @@ patchShebangs() {
         read -r oldInterpreterLine < "$f"
         read -r oldPath arg0 args <<< "${oldInterpreterLine:2}"
 
-        if [[ -z "$pathName" ]]; then
+        if [[ -z "${pathName:-}" ]]; then
             if [[ -n $strictDeps && $f == "$NIX_STORE"* ]]; then
                 pathName=HOST_PATH
             else
diff --git a/pkgs/build-support/setup-hooks/separate-debug-info.sh b/pkgs/build-support/setup-hooks/separate-debug-info.sh
index 334db4cfcd9c..3a16ac4fee90 100644
--- a/pkgs/build-support/setup-hooks/separate-debug-info.sh
+++ b/pkgs/build-support/setup-hooks/separate-debug-info.sh
@@ -21,6 +21,9 @@ _separateDebugInfo() {
     while IFS= read -r -d $'\0' i; do
         if ! isELF "$i"; then continue; fi
 
+        [ -z "${READELF:-}" ] && echo "_separateDebugInfo: '\$READELF' variable is empty, skipping." 1>&2 && break
+        [ -z "${OBJCOPY:-}" ] && echo "_separateDebugInfo: '\$OBJCOPY' variable is empty, skipping." 1>&2 && break
+
         # Extract the Build ID. FIXME: there's probably a cleaner way.
         local id="$($READELF -n "$i" | sed 's/.*Build ID: \([0-9a-f]*\).*/\1/; t; d')"
         if [ "${#id}" != 40 ]; then
diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
index 7c948afc4dac..ad9857fc9d61 100644
--- a/pkgs/stdenv/generic/setup.sh
+++ b/pkgs/stdenv/generic/setup.sh
@@ -1216,7 +1216,7 @@ fixLibtool() {
     done
 
     sed -i "$1" \
-        -e "s^eval \(sys_lib_search_path=\).*^\1'$search_path'^" \
+        -e "s^eval \(sys_lib_search_path=\).*^\1'${search_path:-}'^" \
         -e 's^eval sys_lib_.+search_path=.*^^'
 }