diff --git a/perl/lib/Nix/CopyClosure.pm b/perl/lib/Nix/CopyClosure.pm
index 061a15c07..e12fef6bb 100644
--- a/perl/lib/Nix/CopyClosure.pm
+++ b/perl/lib/Nix/CopyClosure.pm
@@ -100,7 +100,7 @@ sub oldCopyTo {
 
     # Optionally use substitutes on the remote host.
     if (!$dryRun && $useSubstitutes) {
-        system "ssh $sshHost @{$sshOpts} nix-store -r --ignore-unknown @closure";
+        system "ssh $sshHost @{$sshOpts} @globalSshOpts nix-store -r --ignore-unknown @closure";
         # Ignore exit status because this is just an optimisation.
     }
 
@@ -112,7 +112,7 @@ sub oldCopyTo {
     my $missingSize = 0;
     while (scalar(@closure) > 0) {
         my @ps = splice(@closure, 0, 1500);
-        open(READ, "set -f; ssh $sshHost @{$sshOpts} nix-store --check-validity --print-invalid @ps|");
+        open(READ, "set -f; ssh $sshHost @{$sshOpts} @globalSshOpts nix-store --check-validity --print-invalid @ps|");
         while (<READ>) {
             chomp;
             push @missing, $_;
@@ -130,7 +130,7 @@ sub oldCopyTo {
     if (scalar @missing > 0) {
         print STDERR "copying ", scalar @missing, " missing paths to ‘$sshHost’...\n";
         unless ($dryRun) {
-            open SSH, "| $progressViewer $compressor ssh $sshHost @{$sshOpts} '$decompressor nix-store --import' > /dev/null" or die;
+            open SSH, "| $progressViewer $compressor ssh $sshHost @{$sshOpts} @globalSshOpts '$decompressor nix-store --import' > /dev/null" or die;
             exportPaths(fileno(SSH), $sign, @missing);
             close SSH or die "copying store paths to remote machine `$sshHost' failed: $?";
         }
diff --git a/perl/lib/Nix/SSH.pm b/perl/lib/Nix/SSH.pm
index 76a209975..9e0c10beb 100644
--- a/perl/lib/Nix/SSH.pm
+++ b/perl/lib/Nix/SSH.pm
@@ -6,12 +6,16 @@ use IPC::Open2;
 
 our @ISA = qw(Exporter);
 our @EXPORT = qw(
+  @globalSshOpts
   readN readInt readString readStrings
   writeInt writeString writeStrings
   connectToRemoteNix
 );
 
 
+our @globalSshOpts = split ' ', ($ENV{"NIX_SSHOPTS"} or "");
+
+
 sub readN {
     my ($bytes, $from) = @_;
     my $res = "";
@@ -82,7 +86,7 @@ sub connectToRemoteNix {
     # Start ‘nix-store --serve’ on the remote host.
     my ($from, $to);
     # FIXME: don't start a shell, start ssh directly.
-    my $pid = open2($from, $to, "exec ssh -x -a $sshHost @{$sshOpts} nix-store --serve --write $extraFlags");
+    my $pid = open2($from, $to, "exec ssh -x -a $sshHost @globalSshOpts @{$sshOpts} nix-store --serve --write $extraFlags");
 
     # Do the handshake.
     my $SERVE_MAGIC_1 = 0x390c9deb; # FIXME