diff --git a/lib/Slic3r/GCode/PlaceholderParser.pm b/lib/Slic3r/GCode/PlaceholderParser.pm
index d8df755f0..9f45dfe9b 100644
--- a/lib/Slic3r/GCode/PlaceholderParser.pm
+++ b/lib/Slic3r/GCode/PlaceholderParser.pm
@@ -1,4 +1,6 @@
 package Slic3r::GCode::PlaceholderParser;
+use strict;
+use warnings;
 
 sub new {
     # TODO: move this code to C++ constructor, remove this method
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 4e683da41..6d732971b 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -1,4 +1,6 @@
 package Slic3r::Layer;
+use strict;
+use warnings;
 
 use List::Util qw(first);
 use Slic3r::Geometry qw(scale chained_path);
diff --git a/lib/Slic3r/Layer/Region.pm b/lib/Slic3r/Layer/Region.pm
index 976b049fb..ae2a7c2c4 100644
--- a/lib/Slic3r/Layer/Region.pm
+++ b/lib/Slic3r/Layer/Region.pm
@@ -1,4 +1,6 @@
 package Slic3r::Layer::Region;
+use strict;
+use warnings;
 
 use List::Util qw(sum first);
 use Slic3r::ExtrusionLoop ':roles';