diff --git a/debian/llvm-compile-lto-elf.sh b/debian/llvm-compile-lto-elf.sh
index c585f5e4..d0ae0ca3 100644
--- a/debian/llvm-compile-lto-elf.sh
+++ b/debian/llvm-compile-lto-elf.sh
@@ -1,10 +1,25 @@
 #!/usr/bin/bash -eu
 
 # Initial version:
-# https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/rawhide/f/brp-llvm-compile-lto-elf
+# https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/rawhide/f/brp-llvm-compile-lto-elf
 
 CLANG_FLAGS=$@
 
+if test -z $P_TO_LLVM; then
+    echo "P_TO_LLVM isn't set"
+    exit 1
+fi
+
+if test -z $NJOBS; then
+    echo "NJOBS isn't set"
+    exit 1
+fi
+
+if test -z $VERSION; then
+    echo "VERSION isn't set"
+    exit 1
+fi
+
 NCPUS=$NJOBS
 
 check_convert_bitcode () {
@@ -40,6 +55,5 @@ check_convert_bitcode () {
 
 echo "Checking for LLVM bitcode artifacts"
 export -f check_convert_bitcode
-export P
-find "${P_TO_LLVM}/debian/" -type f -name "*.[ao]" -print0 | \
+find "$P_TO_LLVM/debian/" -type f -name "*.[ao]" -print0 | \
   xargs -0 -r -n1 -P$NCPUS bash -c "check_convert_bitcode \$@ $CLANG_FLAGS" ARG0
diff --git a/debian/rules b/debian/rules
index 74e0c3b0..7121da5f 100755
--- a/debian/rules
+++ b/debian/rules
@@ -823,7 +823,7 @@ override_dh_auto_install:
 
 ifeq (${LTO_ENABLE},yes)
 	# with LTO, .a contains llvm ir instead of native code. So, recompile them
-	NJOBS="$(NJOBS)" P_TO_LLVM="$(CURDIR)" VERSION=$(LLVM_VERSION) bash debian/llvm-compile-lto-elf.sh $(CXXFLAGS_EXTRA)
+	NJOBS="$(NJOBS)" P_TO_LLVM="$(CURDIR)" VERSION=$(LLVM_VERSION) bash -v debian/llvm-compile-lto-elf.sh $(CXXFLAGS_EXTRA)
 endif
 
 	# install/fast enables a make install without recompiling temporary files