diff --git a/extensions/Example/template/en/default/setup/strings.txt.pl b/extensions/Example/template/en/default/setup/strings.txt.pl
index 6ee4b5fdcc..01b3edd90b 100644
--- a/extensions/Example/template/en/default/setup/strings.txt.pl
+++ b/extensions/Example/template/en/default/setup/strings.txt.pl
@@ -17,6 +17,9 @@
 # Contributor(s):
 #   Max Kanat-Alexander <mkanat@bugzilla.org>
 
+# This file is loaded inside a Safe compartment, so keep it as plain package
+# data: do not add strict/warnings pragmas or lexical %strings declarations.
+
 %strings = (feature_example_acme => 'Example Extension: Acme Feature',);
 
 1;
diff --git a/extensions/OldBugMove/Config.pm b/extensions/OldBugMove/Config.pm
index e401260469..d2ecc4d249 100644
--- a/extensions/OldBugMove/Config.pm
+++ b/extensions/OldBugMove/Config.pm
@@ -20,6 +20,10 @@
 #   Max Kanat-Alexander <mkanat@bugzilla.org>
 
 package Bugzilla::Extension::OldBugMove;
+
+use 5.14.0;
 use strict;
+use warnings;
+
 use constant NAME => 'OldBugMove';
 __PACKAGE__->NAME;
diff --git a/extensions/OldBugMove/Extension.pm b/extensions/OldBugMove/Extension.pm
index aa3d1aab0e..fae5a4e5ed 100644
--- a/extensions/OldBugMove/Extension.pm
+++ b/extensions/OldBugMove/Extension.pm
@@ -20,7 +20,11 @@
 #   Max Kanat-Alexander <mkanat@bugzilla.org>
 
 package Bugzilla::Extension::OldBugMove;
+
+use 5.14.0;
 use strict;
+use warnings;
+
 use base qw(Bugzilla::Extension);
 use Bugzilla::Constants;
 use Bugzilla::Error;
diff --git a/extensions/OldBugMove/lib/Params.pm b/extensions/OldBugMove/lib/Params.pm
index cea3fecf66..46a9aea118 100644
--- a/extensions/OldBugMove/lib/Params.pm
+++ b/extensions/OldBugMove/lib/Params.pm
@@ -31,7 +31,9 @@
 
 package Bugzilla::Extension::OldBugMove::Params;
 
+use 5.14.0;
 use strict;
+use warnings;
 
 use Bugzilla::Config::Common;
 
diff --git a/extensions/Push/template/en/default/setup/strings.txt.pl b/extensions/Push/template/en/default/setup/strings.txt.pl
index a2a1a1a577..874b3c466b 100644
--- a/extensions/Push/template/en/default/setup/strings.txt.pl
+++ b/extensions/Push/template/en/default/setup/strings.txt.pl
@@ -5,9 +5,8 @@
 # This Source Code Form is "Incompatible With Secondary Licenses", as
 # defined by the Mozilla Public License, v. 2.0.
 
-use strict;
-use warnings;
-use 5.14.0;
+# This file is loaded inside a Safe compartment, so keep it as plain package
+# data: do not add strict/warnings pragmas or lexical %strings declarations.
 
 %strings = (
   feature_push_amqp  => 'Push: AMQP Support',
diff --git a/extensions/ShadowBugs/Config.pm b/extensions/ShadowBugs/Config.pm
index a45948dd4a..9fa46988a8 100644
--- a/extensions/ShadowBugs/Config.pm
+++ b/extensions/ShadowBugs/Config.pm
@@ -6,7 +6,10 @@
 # defined by the Mozilla Public License, v. 2.0.
 
 package Bugzilla::Extension::ShadowBugs;
+
+use 5.14.0;
 use strict;
+use warnings;
 
 use constant NAME             => 'ShadowBugs';
 use constant REQUIRED_MODULES => [];
diff --git a/extensions/ShadowBugs/Extension.pm b/extensions/ShadowBugs/Extension.pm
index 28693c07ee..5337c98886 100644
--- a/extensions/ShadowBugs/Extension.pm
+++ b/extensions/ShadowBugs/Extension.pm
@@ -7,7 +7,9 @@
 
 package Bugzilla::Extension::ShadowBugs;
 
+use 5.14.0;
 use strict;
+use warnings;
 
 use base qw(Bugzilla::Extension);
 
diff --git a/t/Support/Files.pm b/t/Support/Files.pm
index 21f2786d08..626eedb437 100644
--- a/t/Support/Files.pm
+++ b/t/Support/Files.pm
@@ -30,8 +30,13 @@ our @extensions = grep { $_ ne 'extensions/create.pl' && !-e "$_/disabled" }
   glob('extensions/*');
 
 foreach my $extension (@extensions) {
-  find(sub { push(@files, $File::Find::name) if $_ =~ /\.pm$|\.pl$/; },
-    $extension);
+  find(
+    sub {
+      return if $File::Find::name =~ m{^extensions/.+/template/};
+      push(@files, $File::Find::name) if $_ =~ /\.pm$|\.pl$/;
+    },
+    $extension
+  );
 }
 
 our @test_files = glob('t/*.t xt/*/*.t');
diff --git a/template/en/default/filterexceptions.pl b/template/en/default/filterexceptions.pl
index b246fe7372..d118df6215 100644
--- a/template/en/default/filterexceptions.pl
+++ b/template/en/default/filterexceptions.pl
@@ -23,6 +23,9 @@
 # and so do not need to be added here. Doing so will cause warnings.
 # See 008filter.t for more details.
 #
+# This file is loaded by 008filter.t with do(), so keep it as plain package
+# data and avoid strict/warnings pragmas or lexical variable declarations.
+#
 # Comments                        - [%#...
 # Directives                      - [% IF|ELSE|UNLESS|FOREACH...
 # Assignments                     - [% foo = ...
diff --git a/template/en/default/setup/strings.txt.pl b/template/en/default/setup/strings.txt.pl
index 54974aadb3..1627e1f70b 100644
--- a/template/en/default/setup/strings.txt.pl
+++ b/template/en/default/setup/strings.txt.pl
@@ -9,6 +9,9 @@
 # installation code to display strings before Template-Toolkit can safely
 # be loaded.
 #
+# This file is loaded inside a Safe compartment, so keep it as plain package
+# data: do not add strict/warnings pragmas or lexical %strings declarations.
+#
 # Each string supports a very simple substitution system, where you can
 # have variables named like ##this## and they'll be replaced by the string
 # variable with that name.