diff --git a/lib/http/cookie.rb b/lib/http/cookie.rb
index 6f56acd..bdd84db 100644
--- a/lib/http/cookie.rb
+++ b/lib/http/cookie.rb
@@ -564,9 +564,9 @@ class HTTP::Cookie
   def acceptable?
     case
     when @domain.nil?
-      raise ArgumentError, "domain is missing"
+      raise "domain is missing"
     when @path.nil?
-      raise ArgumentError, "path is missing"
+      raise "path is missing"
     when @origin.nil?
       true
     else
@@ -574,8 +574,8 @@ class HTTP::Cookie
     end
   end
 
-  # Tests if it is OK to send this cookie to a given `uri`.  A runtime
-  # error is raised if the cookie's domain is unknown.
+  # Tests if it is OK to send this cookie to a given `uri`.  A
+  # RuntimeError is raised if the cookie's domain is unknown.
   def valid_for_uri?(uri)
     if @domain.nil?
       raise "cannot tell if this cookie is valid because the domain is unknown"
diff --git a/lib/http/cookie_jar.rb b/lib/http/cookie_jar.rb
index ce3e7eb..f1ba2d1 100644
--- a/lib/http/cookie_jar.rb
+++ b/lib/http/cookie_jar.rb
@@ -69,7 +69,12 @@ class HTTP::CookieJar
   #       jar.origin = origin
   #       jar.add(cookie)     # acceptance check is performed
   def add(cookie)
-    @store.add(cookie) if cookie.acceptable?
+    @store.add(cookie) if
+      begin
+        cookie.acceptable?
+      rescue RuntimeError => e
+          raise ArgumentError, e.message
+      end
     self
   end
   alias << add
diff --git a/test/test_http_cookie.rb b/test/test_http_cookie.rb
index 160db16..6226fcd 100644
--- a/test/test_http_cookie.rb
+++ b/test/test_http_cookie.rb
@@ -523,7 +523,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal 'key', cookie.name
     assert_equal 'value', cookie.value
     assert_equal nil, cookie.expires
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       cookie.acceptable?
     }
 
@@ -534,7 +534,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal 'key', cookie.name
     assert_equal 'value', cookie.value
     assert_equal expires, cookie.expires
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       cookie.acceptable?
     }
 
@@ -543,7 +543,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal 'value', cookie.value
     assert_equal expires, cookie.expires
     assert_equal false, cookie.for_domain?
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       # domain and path are missing
       cookie.acceptable?
     }
@@ -553,7 +553,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal 'value', cookie.value
     assert_equal expires, cookie.expires
     assert_equal true, cookie.for_domain?
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       # path is missing
       cookie.acceptable?
     }
@@ -563,7 +563,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal 'value', cookie.value
     assert_equal expires, cookie.expires
     assert_equal false, cookie.for_domain?
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       # path is missing
       cookie.acceptable?
     }
@@ -574,7 +574,7 @@ class TestHTTPCookie < Test::Unit::TestCase
     assert_equal expires, cookie.expires
     assert_equal 'example.org', cookie.domain
     assert_equal true, cookie.for_domain?
-    assert_raises(ArgumentError) {
+    assert_raises(RuntimeError) {
       # path is missing
       cookie.acceptable?
     }
@@ -849,7 +849,7 @@ class TestHTTPCookie < Test::Unit::TestCase
       cookie.domain = d
       assert_equal nil, cookie.domain, "domain=#{d.inspect}"
       assert_equal nil, cookie.domain_name, "domain=#{d.inspect}"
-      assert_raises(ArgumentError) {
+      assert_raises(RuntimeError) {
         cookie.acceptable?
       }