diff --git a/bin/pt-ioprofile b/bin/pt-ioprofile
index 0e81b8af..f73b97ef 100755
--- a/bin/pt-ioprofile
+++ b/bin/pt-ioprofile
@@ -870,7 +870,7 @@ main() {
 # Execute the program if it was not included from another file.
 # This makes it possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
 
    # Parse command line options.  We must do this first so we can
    # see if --daemonize was specified.
diff --git a/bin/pt-mysql-summary b/bin/pt-mysql-summary
index 48ea5c9d..8691b59f 100755
--- a/bin/pt-mysql-summary
+++ b/bin/pt-mysql-summary
@@ -2421,7 +2421,7 @@ main() {
 # Execute the program if it was not included from another file.
 # This makes it possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
 
    # Set up temporary dir.
    mk_tmpdir
diff --git a/bin/pt-pmp b/bin/pt-pmp
index eb545746..b8b00dba 100755
--- a/bin/pt-pmp
+++ b/bin/pt-pmp
@@ -215,7 +215,7 @@ main() {
 # Execute the program if it was not included from another file.  This makes it
 # possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
    mk_tmpdir
    main "$@"
    rm_tmpdir
diff --git a/bin/pt-sift b/bin/pt-sift
index 5be9e9b6..16df99ac 100755
--- a/bin/pt-sift
+++ b/bin/pt-sift
@@ -587,7 +587,7 @@ main() {
 # Execute the program if it was not included from another file.  This makes it
 # possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
     main "${@:-""}"
 fi
 
diff --git a/bin/pt-stalk b/bin/pt-stalk
index 3add242b..8adbd5bc 100755
--- a/bin/pt-stalk
+++ b/bin/pt-stalk
@@ -1310,7 +1310,7 @@ main() {
 # Execute the program if it was not included from another file.
 # This makes it possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
 
    # Parse command line options.  We must do this first so we can
    # see if --daemonize was specified.
diff --git a/bin/pt-summary b/bin/pt-summary
index 3fc9c51a..32e864b7 100755
--- a/bin/pt-summary
+++ b/bin/pt-summary
@@ -2289,7 +2289,7 @@ sigtrap() { local PTFUNCNAME=sigtrap;
 # Execute the program if it was not included from another file.  This makes it
 # possible to include without executing, and thus test.
 if    [ "${0##*/}" = "$TOOL" ] \
-   || [ "${0##*/}" = "bash" -a "$_" = "$0" ]; then
+   || [ "${0##*/}" = "bash" -a "${_:-""}" = "$0" ]; then
 
    # Set up temporary dir.
    mk_tmpdir