diff --git a/lib/resolv.rb b/lib/resolv.rb
index bac338c..f8f2b23 100644
--- a/lib/resolv.rb
+++ b/lib/resolv.rb
@@ -3347,7 +3347,31 @@ def initialize(address) # :nodoc:
     attr_reader :address
 
     def to_s # :nodoc:
-      sprintf("%x:%x:%x:%x:%x:%x:%x:%x", *@address.unpack("nnnnnnnn")).sub(/(^|:)0(:0)+(:|$)/, '::')
+      words = @address.unpack("nnnnnnnn")
+
+      # RFC 5952 Section 4.2.3: compress the longest run of two or more
+      # zero fields, choosing the first one when runs are equally long.
+      best_start = best_len = nil
+      i = 0
+      while i < 8
+        if words[i] == 0
+          j = i
+          j += 1 while j < 8 && words[j] == 0
+          if j - i >= 2 && (best_len.nil? || j - i > best_len)
+            best_start, best_len = i, j - i
+          end
+          i = j
+        else
+          i += 1
+        end
+      end
+
+      hex = words.map {|word| sprintf("%x", word) }
+      return hex.join(":") unless best_start
+
+      head = hex[0, best_start].join(":")
+      tail = hex[(best_start + best_len)..-1].join(":")
+      "#{head}::#{tail}"
     end
 
     def inspect # :nodoc:
diff --git a/test/resolv/test_dns.rb b/test/resolv/test_dns.rb
index b8ecef2..8544a0a 100644
--- a/test/resolv/test_dns.rb
+++ b/test/resolv/test_dns.rb
@@ -622,8 +622,12 @@ def test_ipv6_to_s
       ["2001::", "2001::0"],
       ["2001:db8:0:1:1:1:1:1", "2001:db8:0:1:1:1:1:1"], # RFC 5952 Section 4.2.2.
       ["2001:db8::1:1:1:1", "2001:db8:0:0:1:1:1:1"],
-      ["1::1:0:0:0:1", "1:0:0:1:0:0:0:1"],
+      ["1:0:0:1::1", "1:0:0:1:0:0:0:1"], # RFC 5952 Section 4.2.3.
       ["1::1:0:0:1", "1:0:0:0:1:0:0:1"],
+      ["2001:db8::1:0:0:1", "2001:db8:0:0:1:0:0:1"], # RFC 5952 Section 4.2.3.
+      ["2001:0:0:1::", "2001:0:0:1:0:0:0:0"],
+      ["::1:0:0:1", "0:0:0:0:1:0:0:1"],
+      ["1:2:3:4:5:6:7:8", "1:2:3:4:5:6:7:8"],
     ]
 
     test_cases.each do |expected, ipv6|