diff --git a/README.md b/README.md
index 7a0e241..d9e7bef 100644
--- a/README.md
+++ b/README.md
@@ -63,7 +63,7 @@ More configuration parameters:
 - `port`: listen port (default: 24231)
 - `metrics_path`: metrics HTTP endpoint (default: /metrics)
 - `aggregated_metrics_path`: metrics HTTP endpoint (default: /aggregated_metrics)
-- `content_encoding`: encoding format for the exposed metrics (default: identity)
+- `content_encoding`: encoding format for the exposed metrics (default: identity). Supported formats are {identity, gzip}
 
 When using multiple workers, each worker binds to port + `fluent_worker_id`.
 To scrape metrics from all workers at once, you can access http://localhost:24231/aggregated_metrics.
diff --git a/lib/fluent/plugin/in_prometheus.rb b/lib/fluent/plugin/in_prometheus.rb
index 09f4875..9bc01d6 100644
--- a/lib/fluent/plugin/in_prometheus.rb
+++ b/lib/fluent/plugin/in_prometheus.rb
@@ -34,7 +34,7 @@ class PrometheusInput < Fluent::Plugin::Input
     end
 
     desc 'Content encoding of the exposed metrics, Currently supported encoding is identity, gzip. Ref: https://prometheus.io/docs/instrumenting/exposition_formats/#basic-info'
-    config_param :content_encoding, :string, default: "identity"
+    config_param :content_encoding, :enum, list: [:identity, :gzip], default: :identity
 
     def initialize
       super
@@ -58,8 +58,6 @@ def configure(conf)
 
       @base_port = @port
       @port += fluentd_worker_id
-
-      raise "Invalid content encoding for the exposed metrics endpoint" unless @content_encoding="identity" || @content_encoding="gzip"
     end
 
     def multi_workers_ready?
@@ -190,16 +188,7 @@ def start_webrick
     end
 
     def all_metrics
-      body = nil
-      case @content_encoding
-      when 'gzip'
-        gzip = Zlib::GzipWriter.new(StringIO.new)
-        gzip << ::Prometheus::Client::Formats::Text.marshal(@registry)
-        body = gzip.close.string
-      when 'identity'
-        body = ::Prometheus::Client::Formats::Text.marshal(@registry)
-      end
-      [200, { 'Content-Type' => ::Prometheus::Client::Formats::Text::CONTENT_TYPE, 'Content-Encoding' => @content_encoding }, body]
+      response_headers(::Prometheus::Client::Formats::Text.marshal(@registry))
     rescue => e
       [500, { 'Content-Type' => 'text/plain' }, e.to_s]
     end
@@ -212,16 +201,7 @@ def all_workers_metrics
           full_result.add_metrics(resp.body)
         end
       end
-      body = nil
-      case @content_encoding
-      when 'gzip'
-        gzip = Zlib::GzipWriter.new(StringIO.new)
-        gzip << full_result.get_metrics
-        body = gzip.close.string
-      when 'identity'
-        body = full_result.get_metrics
-      end
-      [200, { 'Content-Type' => ::Prometheus::Client::Formats::Text::CONTENT_TYPE, 'Content-Encoding' => @content_encoding }, body]
+      response_headers(full_result.get_metrics)
     rescue => e
       [500, { 'Content-Type' => 'text/plain' }, e.to_s]
     end
@@ -249,5 +229,18 @@ def do_request(host:, port:, secure:)
         yield(http)
       end
     end
+
+    def response_headers(metrics)
+      body = nil
+      case @content_encoding
+      when :gzip
+        gzip = Zlib::GzipWriter.new(StringIO.new)
+        gzip << metrics
+        body = gzip.close.string
+      when :identity
+        body = metrics
+      end
+      [200, { 'Content-Type' => ::Prometheus::Client::Formats::Text::CONTENT_TYPE, 'Content-Encoding' => @content_encoding.to_s }, body]
+    end
   end
 end