diff --git a/NEWS b/NEWS
index 6a78ac6a33..4cb0215587 100644
--- a/NEWS
+++ b/NEWS
@@ -134,6 +134,9 @@ with all sufficient information, see the ChangeLog file or Redmine
 
   * Add Bundler to Standard Library. [Feature #12733]
 
+* DRb
+  * ACL::ACLEntry.new no longer suppresses IPAddr::InvalidPrefixError.
+
 * ERB
   * Add ERB#result_with_hash to render a template with local variables passed
     with a Hash object. [Feature #8631]
diff --git a/lib/drb/acl.rb b/lib/drb/acl.rb
index 7b50644fe4..b004656f09 100644
--- a/lib/drb/acl.rb
+++ b/lib/drb/acl.rb
@@ -49,6 +49,9 @@ class ACL
     # +str+ may be "*" or "all" to match any address, an IP address string
     # to match a specific address, an IP address mask per IPAddr, or one
     # containing "*" to match part of an IPv4 address.
+    #
+    # IPAddr::InvalidPrefixError may be raised when an IP network
+    # address with an invalid netmask/prefix is given.
 
     def initialize(str)
       if str == '*' or str == 'all'
@@ -58,6 +61,10 @@ class ACL
       else
         begin
           @pat = [:ip, IPAddr.new(str)]
+        rescue IPAddr::InvalidPrefixError
+          # In this case, `str` shouldn't be a host name pattern
+          # because it contains a slash.
+          raise
         rescue ArgumentError
           @pat = [:name, dot_pat(str)]
         end
diff --git a/test/drb/test_acl.rb b/test/drb/test_acl.rb
index 6ac89b156b..436ee92207 100644
--- a/test/drb/test_acl.rb
+++ b/test/drb/test_acl.rb
@@ -66,9 +66,9 @@ class ACLEntryTest < Test::Unit::TestCase
     assert_not_operator(a, :match, @hosts['localhost'])
     assert_operator(a, :match, @hosts['yum'])
 
-    a = ACL::ACLEntry.new('192.168.0.1/255.255.0.255')
+    a = ACL::ACLEntry.new('192.168.1.0/255.255.255.0')
     assert_not_operator(a, :match, @hosts['localhost'])
-    assert_not_operator(a, :match, @hosts['yum'])
+    assert_operator(a, :match, @hosts['yum'])
     assert_operator(a, :match, @hosts['x68k'])
 
     a = ACL::ACLEntry.new('192.168.1.0/24')
@@ -81,10 +81,14 @@ class ACLEntryTest < Test::Unit::TestCase
     assert_not_operator(a, :match, @hosts['yum'])
     assert_not_operator(a, :match, @hosts['x68k'])
 
-    a = ACL::ACLEntry.new('127.0.0.1/255.0.0.255')
+    a = ACL::ACLEntry.new('127.0.0.0/255.0.0.0')
     assert_operator(a, :match, @hosts['localhost'])
     assert_not_operator(a, :match, @hosts['yum'])
     assert_not_operator(a, :match, @hosts['x68k'])
+
+    assert_raise(IPAddr::InvalidPrefixError) {
+      ACL::ACLEntry.new('192.168.0.0/33')
+    }
   end
 
   def test_name
@@ -136,10 +140,12 @@ class ACLListTest < Test::Unit::TestCase
   end
 
   def test_1
-    a = build(%w(192.0.0.1/255.0.0.255 yum.*.jp))
-    assert_operator(a, :match, @hosts['yum'])
+    a = build(%w(192.168.1.0/255.255.255.252 yum.*.jp))
     assert_operator(a, :match, @hosts['x68k'])
-    assert_not_operator(a, :match, @hosts['lc630'])
+    assert_operator(a, :match, @hosts['lc630'])
+    assert_operator(a, :match, @hosts['lib30'])
+    assert_not_operator(a, :match, @hosts['ns00'])
+    assert_operator(a, :match, @hosts['yum'])
   end
 
   def test_2