diff --git a/spec/cases/count_open_pipes.rb b/spec/cases/count_open_pipes.rb
index 2649966..7565e66 100644
--- a/spec/cases/count_open_pipes.rb
+++ b/spec/cases/count_open_pipes.rb
@@ -1,6 +1,21 @@
 # frozen_string_literal: true
 require './spec/cases/helper'
-count = ->(*) { `lsof -l | grep pipe | wc -l`.to_i }
+count = ->(*) { Dir.children("/dev/fd").size }
+
+if ENV["SELF_TEST"]
+  # verify that count detects newly opened pipes
+  create = 5
+  before = count.call
+  pipes = create.times.map { IO.pipe }
+  after = count.call
+  expected = before + (create * 2)
+  raise "expected #{expected} fds but got #{after}" unless after == expected
+  pipes.each do |r, w|
+    r.close
+    w.close
+  end
+end
+
 start = count.call
 results = Parallel.map(Array.new(20), in_processes: 20, &count)
 puts results.max - start
diff --git a/spec/cases/helper.rb b/spec/cases/helper.rb
index b2f9b92..ac223e4 100644
--- a/spec/cases/helper.rb
+++ b/spec/cases/helper.rb
@@ -10,7 +10,7 @@ def process_diff
 
   yield
 
-  sleep 1
+  sleep 0.5
 
   processes_after = `#{cmd}`.to_i
 
diff --git a/spec/cases/parallel_high_fork_rate.rb b/spec/cases/parallel_high_fork_rate.rb
index 1f3b4e7..4b93b23 100644
--- a/spec/cases/parallel_high_fork_rate.rb
+++ b/spec/cases/parallel_high_fork_rate.rb
@@ -2,6 +2,6 @@
 require './spec/cases/helper'
 
 Parallel.each((0..200).to_a, in_processes: 200) do |_x|
-  sleep 1
+  sleep 0.1
 end
 print 'OK'
diff --git a/spec/cases/parallel_map_uneven.rb b/spec/cases/parallel_map_uneven.rb
index cb18f9e..4ef073d 100644
--- a/spec/cases/parallel_map_uneven.rb
+++ b/spec/cases/parallel_map_uneven.rb
@@ -2,5 +2,5 @@
 require './spec/cases/helper'
 
 Parallel.map([1, 2, 1, 2]) do |x|
-  sleep 2 if x == 1
+  sleep 1 if x == 1
 end
diff --git a/spec/cases/parallel_sleeping_2.rb b/spec/cases/parallel_sleeping_2.rb
index c2c42c3..051b676 100644
--- a/spec/cases/parallel_sleeping_2.rb
+++ b/spec/cases/parallel_sleeping_2.rb
@@ -2,5 +2,5 @@
 require './spec/cases/helper'
 
 Parallel.in_processes(5) do
-  sleep 2
+  sleep 1
 end
diff --git a/spec/cases/progress.rb b/spec/cases/progress.rb
index 5f98f1d..a324660 100644
--- a/spec/cases/progress.rb
+++ b/spec/cases/progress.rb
@@ -2,6 +2,6 @@
 require './spec/cases/helper'
 
 title = (ENV["TITLE"] == "true" ? true : "Doing stuff")
-Parallel.map(1..50, progress: title) do
+Parallel.map(1..10, progress: title) do
   sleep 1 if $stdout.tty? # for debugging
 end
diff --git a/spec/cases/progress_with_finish.rb b/spec/cases/progress_with_finish.rb
index 0aed71f..437f520 100644
--- a/spec/cases/progress_with_finish.rb
+++ b/spec/cases/progress_with_finish.rb
@@ -4,7 +4,7 @@
 sum = 0
 finish = ->(_item, _index, result) { sum += result }
 
-Parallel.map(1..50, progress: "Doing stuff", finish: finish) do
+Parallel.map(1..10, progress: "Doing stuff", finish: finish) do
   sleep 1 if $stdout.tty? # for debugging
   2
 end
diff --git a/spec/cases/with_worker_number.rb b/spec/cases/with_worker_number.rb
index 8a9976e..f7fdff8 100644
--- a/spec/cases/with_worker_number.rb
+++ b/spec/cases/with_worker_number.rb
@@ -4,7 +4,7 @@
 method = ENV.fetch('METHOD')
 in_worker_type = :"in_#{ENV.fetch('WORKER_TYPE')}"
 
-Parallel.public_send(method, 1..100, in_worker_type => 4) do
-  sleep 0.1 # so all workers get started
+Parallel.public_send(method, 1..20, in_worker_type => 4) do
+  sleep 0.02 # so all workers get started
   print Parallel.worker_number
 end
diff --git a/spec/parallel_spec.rb b/spec/parallel_spec.rb
index d2093fa..fcb330a 100644
--- a/spec/parallel_spec.rb
+++ b/spec/parallel_spec.rb
@@ -161,7 +161,7 @@ def cpus
     it "saves time" do
       time_taken do
         ruby("spec/cases/parallel_sleeping_2.rb")
-      end.should < 3.5
+      end.should < 2.5
     end
 
     it "raises when one of the processes raises" do
@@ -203,12 +203,12 @@ def cpus
   describe ".in_threads" do
     it "saves time" do
       time_taken do
-        Parallel.in_threads(3) { sleep 2 }
-      end.should < 3
+        Parallel.in_threads(3) { sleep 1 }
+      end.should < 2
     end
 
     it "does not create new processes" do
-      -> { Thread.new { Parallel.in_threads(2) { sleep 1 } } }.should_not(change { `ps`.split("\n").size })
+      -> { Thread.new { Parallel.in_threads(2) { sleep 0.5 } } }.should_not(change { `ps`.split("\n").size })
     end
 
     it "returns results as array" do
@@ -245,7 +245,7 @@ def cpus
     it "starts new process immediately when old exists" do
       time_taken do
         ruby("spec/cases/parallel_map_uneven.rb")
-      end.should <= 3.5
+      end.should <= 2.5
     end
 
     it "does not flatten results" do
@@ -661,7 +661,7 @@ def cpus
       ruby("spec/cases/progress_with_finish.rb 2>&1").strip.sub(/=+/, '==').gsub(
         /\n+/,
         "\n"
-      ).should == "Doing stuff: |==|\n100"
+      ).should == "Doing stuff: |==|\n20"
     end
 
     it "takes the title from :progress[:title] and passes options along" do