diff --git a/etc/profile.d/z-aliases.sh b/etc/profile.d/z-aliases.sh
index ac8c32e..342c14d 100755
--- a/etc/profile.d/z-aliases.sh
+++ b/etc/profile.d/z-aliases.sh
@@ -1,3 +1,8 @@
+if [ "${BASH_SOURCE-}" = "$0" ]; then
+    echo -e "You must source this script:\n\tsource $0" >&2
+    exit 33
+fi
+
 # show hidden files and directories
 alias l.='ls -d .[^.]* ..?* --color=tty 2>/dev/null'
 
diff --git a/etc/profile.d/z-env.sh b/etc/profile.d/z-env.sh
index fe82f50..2d51b39 100755
--- a/etc/profile.d/z-env.sh
+++ b/etc/profile.d/z-env.sh
@@ -1,3 +1,8 @@
+if [ "${BASH_SOURCE-}" = "$0" ]; then
+    echo -e "You must source this script:\n\tsource $0" >&2
+    exit 33
+fi
+
 EDITOR=mcedit
 export EDITOR
 
diff --git a/etc/profile.d/z-ps-twtty-7.sh b/etc/profile.d/z-ps-twtty-7.sh
index 754eba4..de02975 100755
--- a/etc/profile.d/z-ps-twtty-7.sh
+++ b/etc/profile.d/z-ps-twtty-7.sh
@@ -42,6 +42,11 @@
 #   - http://www.onerussian.com/Linux/bash_history.phtml
 #   - https://debian-administration.org/article/175/BASH_history_forever.
 
+if [ "${BASH_SOURCE-}" = "$0" ]; then
+    echo -e "You must source this script:\n\tsource $0" >&2
+    exit 33
+fi
+
 if [ "$PS1" ] ; then # interactive shell detection
 
 # Log the logout event.
diff --git a/etc/profile.d/z-time_style.sh b/etc/profile.d/z-time_style.sh
index 1412474..9c47dca 100755
--- a/etc/profile.d/z-time_style.sh
+++ b/etc/profile.d/z-time_style.sh
@@ -1,2 +1,7 @@
+if [ "${BASH_SOURCE-}" = "$0" ]; then
+    echo -e "You must source this script:\n\tsource $0" >&2
+    exit 33
+fi
+
 TIME_STYLE=long-iso
 export TIME_STYLE