diff --git a/lib/fluent/plugin/filter_grep.rb b/lib/fluent/plugin/filter_grep.rb
index d289de70f2..87a5d378e6 100644
--- a/lib/fluent/plugin/filter_grep.rb
+++ b/lib/fluent/plugin/filter_grep.rb
@@ -41,7 +41,11 @@ def initialize
       config_param :key, :string
       desc "The regular expression."
       config_param :pattern do |value|
-        Regexp.compile(value)
+        if value.start_with?("/") and value.end_with?("/")
+          Regexp.compile(value[1..-2])
+        else
+          Regexp.compile(value)
+        end
       end
     end
 
@@ -50,7 +54,11 @@ def initialize
       config_param :key, :string
       desc "The regular expression."
       config_param :pattern do |value|
-        Regexp.compile(value)
+        if value.start_with?("/") and value.end_with("/")
+          Regexp.compile(value[1..-2])
+        else
+          Regexp.compile(value)
+        end
       end
     end
 
diff --git a/test/plugin/test_filter_grep.rb b/test/plugin/test_filter_grep.rb
index 2eb6dba178..18a40cd198 100644
--- a/test/plugin/test_filter_grep.rb
+++ b/test/plugin/test_filter_grep.rb
@@ -73,6 +73,19 @@ def create_driver(conf = '')
         end
       end
     end
+
+    sub_test_case "pattern with slashes" do
+      test "start with character classes" do
+        conf = %[
+          <regexp>
+            key message
+            pattern /[a-z]test/
+          </regexp>
+        ]
+        d = create_driver(conf)
+        assert_equal(/[a-z]test/, d.instance.regexps.first.pattern)
+      end
+    end
   end
 
   sub_test_case 'filter_stream' do