diff --git a/lib/http/cookie_jar/abstract_store.rb b/lib/http/cookie_jar/abstract_store.rb
index 6734854..0f45690 100644
--- a/lib/http/cookie_jar/abstract_store.rb
+++ b/lib/http/cookie_jar/abstract_store.rb
@@ -1,4 +1,8 @@
+require 'monitor'
+
 class HTTP::CookieJar::AbstractStore
+  include MonitorMixin
+
   class << self
     @@class_map = {}
 
@@ -31,6 +35,7 @@ class HTTP::CookieJar::AbstractStore
   private :default_options
 
   def initialize(options = nil)
+    super() # MonitorMixin
     options ||= {}
     @logger = options[:logger]
     # Initializes each instance variable of the same name as option
@@ -65,7 +70,13 @@ class HTTP::CookieJar::AbstractStore
   # If (and only if) the +uri+ option is given, last access time of
   # each cookie is updated to the current time.
   def each(uri = nil, &block)
-    raise
+    if uri
+      raise
+    else
+      synchronize {
+        raise
+      }
+    end
     self
   end
   include Enumerable
diff --git a/lib/http/cookie_jar/hash_store.rb b/lib/http/cookie_jar/hash_store.rb
index ccd6a55..4332986 100644
--- a/lib/http/cookie_jar/hash_store.rb
+++ b/lib/http/cookie_jar/hash_store.rb
@@ -81,15 +81,17 @@ class HTTP::CookieJar
           }
         }
       else
-        @jar.each { |domain, paths|
-          paths.each { |path, hash|
-            hash.delete_if { |name, cookie|
-              if cookie.expired?(now)
-                true
-              else
-                yield cookie
-                false
-              end
+        synchronize {
+          @jar.each { |domain, paths|
+            paths.each { |path, hash|
+              hash.delete_if { |name, cookie|
+                if cookie.expired?(now)
+                  true
+                else
+                  yield cookie
+                  false
+                end
+              }
             }
           }
         }
@@ -109,45 +111,51 @@ class HTTP::CookieJar
     def cleanup(session = false)
       now = Time.now
       all_cookies = []
-      @jar.each { |domain, paths|
-        domain_cookies = []
 
-        paths.each { |path, hash|
-          hash.delete_if { |name, cookie|
-            if cookie.expired?(now) || (session && cookie.session?)
-              true
-            else
-              domain_cookies << cookie
-              false
-            end
+      synchronize {
+        break if @gc_index == 0
+
+        @jar.each { |domain, paths|
+          domain_cookies = []
+
+          paths.each { |path, hash|
+            hash.delete_if { |name, cookie|
+              if cookie.expired?(now) || (session && cookie.session?)
+                true
+              else
+                domain_cookies << cookie
+                false
+              end
+            }
           }
+
+          if (debt = domain_cookies.size - HTTP::Cookie::MAX_COOKIES_PER_DOMAIN) > 0
+            domain_cookies.sort_by!(&:created_at)
+            domain_cookies.slice!(0, debt).each { |cookie|
+              delete(cookie)
+            }
+          end
+
+          all_cookies.concat(domain_cookies)
         }
 
-        if (debt = domain_cookies.size - HTTP::Cookie::MAX_COOKIES_PER_DOMAIN) > 0
-          domain_cookies.sort_by!(&:created_at)
-          domain_cookies.slice!(0, debt).each { |cookie|
+        if (debt = all_cookies.size - HTTP::Cookie::MAX_COOKIES_TOTAL) > 0
+          all_cookies.sort_by!(&:created_at)
+          all_cookies.slice!(0, debt).each { |cookie|
             delete(cookie)
           }
         end
 
-        all_cookies.concat(domain_cookies)
-      }
-
-      if (debt = all_cookies.size - HTTP::Cookie::MAX_COOKIES_TOTAL) > 0
-        all_cookies.sort_by!(&:created_at)
-        all_cookies.slice!(0, debt).each { |cookie|
-          delete(cookie)
+        @jar.delete_if { |domain, paths|
+          paths.delete_if { |path, hash|
+            hash.empty?
+          }
+          paths.empty?
         }
-      end
 
-      @jar.delete_if { |domain, paths|
-        paths.delete_if { |path, hash|
-          hash.empty?
-        }
-        paths.empty?
+        @gc_index = 0
       }
-
-      @gc_index = 0
+      self
     end
   end
 end
diff --git a/lib/http/cookie_jar/mozilla_store.rb b/lib/http/cookie_jar/mozilla_store.rb
index a381f33..67e950d 100644
--- a/lib/http/cookie_jar/mozilla_store.rb
+++ b/lib/http/cookie_jar/mozilla_store.rb
@@ -335,9 +335,6 @@ class HTTP::CookieJar
     end
 
     def cleanup(session = false)
-      now = Time.now
-      all_cookies = []
-
       @st_delete_expired ||=
         @db.prepare("DELETE FROM moz_cookies WHERE expiry < :expiry")
 
@@ -364,26 +361,31 @@ class HTTP::CookieJar
                      )
         SQL
 
-      @st_delete_expired.execute({ 'expiry' => now.to_i })
+      synchronize {
+        break if @gc_index == 0
 
-      @st_overusing_domains.execute({
-          'count' => HTTP::Cookie::MAX_COOKIES_PER_DOMAIN
-        }).each { |row|
-        domain, count = row['domain'], row['count']
+        @st_delete_expired.execute({ 'expiry' => Time.now.to_i })
 
-        @st_delete_per_domain_overuse.execute({
-            'domain' => domain,
-            'limit' => count - HTTP::Cookie::MAX_COOKIES_PER_DOMAIN,
-          })
+        @st_overusing_domains.execute({
+            'count' => HTTP::Cookie::MAX_COOKIES_PER_DOMAIN
+          }).each { |row|
+          domain, count = row['domain'], row['count']
+
+          @st_delete_per_domain_overuse.execute({
+              'domain' => domain,
+              'limit' => count - HTTP::Cookie::MAX_COOKIES_PER_DOMAIN,
+            })
+        }
+
+        overrun = count - HTTP::Cookie::MAX_COOKIES_TOTAL
+
+        if overrun > 0
+          @st_delete_total_overuse.execute({ 'limit' => overrun })
+        end
+
+        @gc_index = 0
       }
-
-      overrun = count - HTTP::Cookie::MAX_COOKIES_TOTAL
-
-      if overrun > 0
-        @st_delete_total_overuse.execute({ 'limit' => overrun })
-      end
-
-      @gc_index = 0
+      self
     end
   end
 end