diff --git a/t/HTTP-Server-PSGI/harakiri.t b/t/HTTP-Server-PSGI/harakiri.t
index f104f9a0e..9f5613f38 100644
--- a/t/HTTP-Server-PSGI/harakiri.t
+++ b/t/HTTP-Server-PSGI/harakiri.t
@@ -1,11 +1,18 @@
 use strict;
 use warnings;
 
+use Config;
 use Plack::Runner;
 use Test::More;
 use Test::TCP;
 use Test::Requires qw(LWP::UserAgent);
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 my $ua_timeout = 3;
 
 test_tcp(
diff --git a/t/HTTP-Server-PSGI/post.t b/t/HTTP-Server-PSGI/post.t
index 20af84ee2..a56d2bb07 100644
--- a/t/HTTP-Server-PSGI/post.t
+++ b/t/HTTP-Server-PSGI/post.t
@@ -1,11 +1,18 @@
 use strict;
 use warnings;
 
+use Config;
 use Plack::Runner;
 use Test::More;
 use Test::TCP;
 use Test::Requires qw(LWP::UserAgent);
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 test_tcp(
     server => sub {
         my $port = shift;
diff --git a/t/Plack-Handler/standalone.t b/t/Plack-Handler/standalone.t
index f5fcf266f..4a516ece3 100644
--- a/t/Plack-Handler/standalone.t
+++ b/t/Plack-Handler/standalone.t
@@ -1,8 +1,15 @@
 use strict;
 use warnings;
+use Config;
 use Test::More;
 use Plack::Test::Suite;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 Plack::Test::Suite->run_server_tests('Standalone');
 done_testing();
 
diff --git a/t/Plack-Middleware/component-leak.t b/t/Plack-Middleware/component-leak.t
index 7cdab9914..3563fef1b 100644
--- a/t/Plack-Middleware/component-leak.t
+++ b/t/Plack-Middleware/component-leak.t
@@ -1,10 +1,17 @@
 package MyComponent;
 use strict;
 use warnings;
+use Config;
 use Test::More;
 use Scalar::Util qw/weaken/;
 use parent 'Plack::Component';
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 sub call {
     my $self = shift;
     my $env = shift;
diff --git a/t/Plack-Middleware/error_document_streaming_app.t b/t/Plack-Middleware/error_document_streaming_app.t
index b177c536f..d031ef3c8 100644
--- a/t/Plack-Middleware/error_document_streaming_app.t
+++ b/t/Plack-Middleware/error_document_streaming_app.t
@@ -1,11 +1,18 @@
 use strict;
 use warnings;
+use Config;
 use FindBin;
 use Test::More;
 use HTTP::Request::Common;
 use Plack::Test;
 use Plack::Builder;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = undef;
 my @impl = ('Server', 'MockHTTP');
 sub flip_backend {
diff --git a/t/Plack-Middleware/stacktrace/sigdie.t b/t/Plack-Middleware/stacktrace/sigdie.t
index dc82b2c74..587154aa3 100644
--- a/t/Plack-Middleware/stacktrace/sigdie.t
+++ b/t/Plack-Middleware/stacktrace/sigdie.t
@@ -1,10 +1,17 @@
 use strict;
 use warnings;
+use Config;
 use Test::More;
 use Plack::Middleware::StackTrace;
 use Plack::Test;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Middleware/stacktrace/utf8.t b/t/Plack-Middleware/stacktrace/utf8.t
index 6d2f51fff..92aedd2d1 100644
--- a/t/Plack-Middleware/stacktrace/utf8.t
+++ b/t/Plack-Middleware/stacktrace/utf8.t
@@ -1,11 +1,18 @@
 use strict;
 use warnings;
+use Config;
 use Test::More;
 use Test::Requires { 'Devel::StackTrace::AsHTML' => 0.08 };
 use Plack::Middleware::StackTrace;
 use Plack::Test;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Middleware/urlmap_ports.t b/t/Plack-Middleware/urlmap_ports.t
index 9a0a9c0a6..de82db78a 100644
--- a/t/Plack-Middleware/urlmap_ports.t
+++ b/t/Plack-Middleware/urlmap_ports.t
@@ -1,9 +1,16 @@
 use strict;
+use Config;
 use Test::More;
 use Plack::App::URLMap;
 use Plack::Test;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Request/double_port.t b/t/Plack-Request/double_port.t
index b5ffdd4ad..d8207897d 100644
--- a/t/Plack-Request/double_port.t
+++ b/t/Plack-Request/double_port.t
@@ -1,8 +1,15 @@
+use Config;
 use Test::More;
 use Plack::Test;
 use Plack::Request;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = 'Server';
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Request/upload-large.t b/t/Plack-Request/upload-large.t
index 327a83ace..d64b7cb28 100644
--- a/t/Plack-Request/upload-large.t
+++ b/t/Plack-Request/upload-large.t
@@ -1,10 +1,17 @@
 use strict;
 use warnings;
+use Config;
 use Test::More;
 use Plack::Request;
 use Plack::Test;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 my $file = "share/baybridge.jpg";
 
 my @backends = qw( Server MockHTTP );
diff --git a/t/Plack-Test/2args.t b/t/Plack-Test/2args.t
index 2942f93b3..79af11349 100644
--- a/t/Plack-Test/2args.t
+++ b/t/Plack-Test/2args.t
@@ -1,6 +1,14 @@
+use Config;
 use Plack::Test;
 use Test::More;
 use HTTP::Request::Common;
+
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Test/hello_server.t b/t/Plack-Test/hello_server.t
index 47ffb75bc..ad03086d2 100644
--- a/t/Plack-Test/hello_server.t
+++ b/t/Plack-Test/hello_server.t
@@ -1,6 +1,13 @@
+use Config;
 use Test::More;
 use Plack::Test;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 local $ENV{PLACK_SERVER} = "HTTP::Server::PSGI";
 
diff --git a/t/Plack-Util/response_cb.t b/t/Plack-Util/response_cb.t
index 813dc871a..34c85cc08 100644
--- a/t/Plack-Util/response_cb.t
+++ b/t/Plack-Util/response_cb.t
@@ -1,10 +1,17 @@
 use strict;
 use warnings;
+use Config;
 use Plack::Util;
 use Plack::Test;
 use Test::More;
 use HTTP::Request::Common;
 
+plan skip_all => "fork not supported on this platform"
+  unless $Config::Config{d_fork} || $Config::Config{d_pseudofork} ||
+    (($^O eq 'MSWin32' || $^O eq 'NetWare') and
+     $Config::Config{useithreads} and
+     $Config::Config{ccflags} =~ /-DPERL_IMPLICIT_SYS/);
+
 $Plack::Test::Impl = "Server";
 
 my $app = sub {