diff --git a/src/lib/Hydra/Helper/Nix.pm b/src/lib/Hydra/Helper/Nix.pm
index bac90b85..e1c56b06 100644
--- a/src/lib/Hydra/Helper/Nix.pm
+++ b/src/lib/Hydra/Helper/Nix.pm
@@ -141,8 +141,8 @@ sub registerRoot {
     my ($path) = @_;
     my $link = gcRootFor $path;
     return if -e $link;
-    open ROOT, ">$link" or die "cannot create GC root `$link' to `$path'";
-    close ROOT;
+    open my $root, ">$link" or die "cannot create GC root `$link' to `$path'";
+    close $root;
 }
 
 
@@ -341,8 +341,8 @@ sub getMachines {
 
     for my $machinesFile (@machinesFiles) {
         next unless -e $machinesFile;
-        open CONF, "<$machinesFile" or die;
-        while (<CONF>) {
+        open my $conf, "<$machinesFile" or die;
+        while (<$conf>) {
             chomp;
             s/\#.*$//g;
             next if /^\s*$/;
@@ -358,7 +358,7 @@ sub getMachines {
                 , mandatoryFeatures => [ @mandatoryFeatures ]
                 };
         }
-        close CONF;
+        close $conf;
     }
 
     return \%machines;
diff --git a/src/lib/Hydra/Plugin/CoverityScan.pm b/src/lib/Hydra/Plugin/CoverityScan.pm
index 53f7c3f6..fcedf92a 100644
--- a/src/lib/Hydra/Plugin/CoverityScan.pm
+++ b/src/lib/Hydra/Plugin/CoverityScan.pm
@@ -52,12 +52,12 @@ sub buildFinished {
     my $tarballs  = "$storePath/tarballs";
     my $covTarball;
 
-    opendir TARBALLS, $tarballs or die;
-    while (readdir TARBALLS) {
+    opendir my $tarballs_handle, $tarballs or die;
+    while (readdir $tarballshandle) {
         next unless $_ =~ /.*-coverity-int\.(tgz|lzma|xz|bz2|zip)$/;
         $covTarball = "$tarballs/$_"; last;
     }
-    closedir TARBALLS;
+    closedir $tarballs_handle;
 
     unless (defined $covTarball) {
         print STDERR "CoverityScan.pm: Coverity tarball not found in $tarballs; skipping upload...\n";
diff --git a/src/script/hydra-s3-backup-collect-garbage b/src/script/hydra-s3-backup-collect-garbage
index b8394518..23b50c2f 100755
--- a/src/script/hydra-s3-backup-collect-garbage
+++ b/src/script/hydra-s3-backup-collect-garbage
@@ -26,9 +26,9 @@ my $client = Net::Amazon::S3::Client->new( s3 => Net::Amazon::S3->new( retry =>
 my $db = Hydra::Model::DB->new();
 
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-my @roots = readdir DIR;
-closedir DIR;
+opendir my $dir, $gcRootsDir or die;
+my @roots = readdir $dir;
+closedir $dir;
 
 my @actual_roots = ();
 foreach my $link (@roots) {
diff --git a/src/script/hydra-update-gc-roots b/src/script/hydra-update-gc-roots
index 69578e29..b8ddf971 100755
--- a/src/script/hydra-update-gc-roots
+++ b/src/script/hydra-update-gc-roots
@@ -63,9 +63,9 @@ sub keepBuild {
 # Read the current GC roots.
 print STDERR "*** reading current roots...\n";
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-my @roots = readdir DIR;
-closedir DIR;
+opendir my $dir, $gcRootsDir or die;
+my @roots = readdir $dir;
+closedir $dir;
 
 
 # For scheduled builds, we register the derivation as a GC root.
diff --git a/t/s3-backup-test.pl b/t/s3-backup-test.pl
index 3baa8b99..825162d3 100644
--- a/t/s3-backup-test.pl
+++ b/t/s3-backup-test.pl
@@ -39,12 +39,12 @@ ok(-e "/tmp/s3/hydra/$successful_hash.nar", "The nar of a build that's a root is
 ok(-e "/tmp/s3/hydra/$successful_hash.narinfo", "The narinfo of a build that's a root is not removed by gc");
 
 my $gcRootsDir = getGCRootsDir;
-opendir DIR, $gcRootsDir or die;
-while(readdir DIR) {
+opendir my $dir, $gcRootsDir or die;
+while(readdir $dir) {
     next if $_ eq "." or $_ eq "..";
     unlink "$gcRootsDir/$_";
 }
-closedir DIR;
+closedir $dir;
 system("hydra-s3-backup-collect-garbage");
 ok(not -e "/tmp/s3/hydra/$successful_hash.nar", "The nar of a build that's not a root is removed by gc");
 ok(not -e "/tmp/s3/hydra/$successful_hash.narinfo", "The narinfo of a build that's not a root is removed by gc");