diff --git a/Logtalk/scripts/lgt_install.sh b/Logtalk/scripts/lgt_install.sh
index f255c4492..3bb4bff61 100755
--- a/Logtalk/scripts/lgt_install.sh
+++ b/Logtalk/scripts/lgt_install.sh
@@ -13,7 +13,7 @@ else
 	prefix="$1"
 fi
 
-if ! [ -d "$1" ]; then
+if ! [ -d "$prefix" ]; then
 	echo "Directory prefix does not exist!"
 	echo
 	exit 1
diff --git a/Logtalk/scripts/makeall_lgt.sh b/Logtalk/scripts/makeall_lgt.sh
index a8d1dc0a8..57309e8f6 100755
--- a/Logtalk/scripts/makeall_lgt.sh
+++ b/Logtalk/scripts/makeall_lgt.sh
@@ -24,7 +24,7 @@ else
 	prefix="$1"
 fi
 
-if ! [ -d "$1" ]; then
+if ! [ -d "$prefix" ]; then
 	echo "Directory prefix does not exist!"
 	echo
 	exit 1