diff --git a/fhem/FHEM/38_CO20.pm b/fhem/FHEM/38_CO20.pm
index 649db875f..c1bd6a6d1 100755
--- a/fhem/FHEM/38_CO20.pm
+++ b/fhem/FHEM/38_CO20.pm
@@ -8,9 +8,11 @@ package main;
 use strict;
 use warnings;
 
-$ENV{CFLAGS} = '';
-$ENV{CPPFLAGS} = '';
-$ENV{LDFLAGS} = '';
+BEGIN {
+  $ENV{CFLAGS} = '';
+  $ENV{CPPFLAGS} = '';
+  $ENV{LDFLAGS} = '';
+}
 
 use Device::USB;