diff --git a/lib/oauth/request_proxy/base.rb b/lib/oauth/request_proxy/base.rb
index a8411cb3..3cc628b9 100644
--- a/lib/oauth/request_proxy/base.rb
+++ b/lib/oauth/request_proxy/base.rb
@@ -23,15 +23,15 @@ def initialize(request, options = {})
       ## OAuth parameters
 
       def oauth_callback
-        parameters["oauth_callback"]
+        [parameters["oauth_callback"]].flatten.first
       end
 
       def oauth_consumer_key
-        parameters["oauth_consumer_key"]
+        [parameters["oauth_consumer_key"]].flatten.first
       end
 
       def oauth_nonce
-        parameters["oauth_nonce"]
+        [parameters["oauth_nonce"]].flatten.first
       end
 
       def oauth_signature
@@ -40,31 +40,26 @@ def oauth_signature
       end
 
       def oauth_signature_method
-        case parameters["oauth_signature_method"]
-        when Array
-          parameters["oauth_signature_method"].first
-        else
-          parameters["oauth_signature_method"]
-        end
+        [parameters["oauth_signature_method"]].flatten.first
       end
 
       def oauth_timestamp
-        parameters["oauth_timestamp"]
+        [parameters["oauth_timestamp"]].flatten.first
       end
 
       def oauth_token
-        parameters["oauth_token"]
+        [parameters["oauth_token"]].flatten.first
       end
 
       # OAuth 1.0a only: value returned to the Consumer after user authorization
       # and required when exchanging a Request Token for an Access Token.
       # Not present in OAuth 1.0 flows.
       def oauth_verifier
-        parameters["oauth_verifier"]
+        [parameters["oauth_verifier"]].flatten.first
       end
 
       def oauth_version
-        parameters["oauth_version"]
+        [parameters["oauth_version"]].flatten.first
       end
 
       # TODO: deprecate these
diff --git a/lib/oauth/request_proxy/rack_request.rb b/lib/oauth/request_proxy/rack_request.rb
index f006fc4a..f35c1f42 100644
--- a/lib/oauth/request_proxy/rack_request.rb
+++ b/lib/oauth/request_proxy/rack_request.rb
@@ -26,10 +26,6 @@ def parameters
         end
       end
 
-      def signature
-        parameters["oauth_signature"]
-      end
-
       protected
 
       def query_params
diff --git a/spec/oauth/request_proxy/base_accessors_spec.rb b/spec/oauth/request_proxy/base_accessors_spec.rb
new file mode 100644
index 00000000..f01f12b8
--- /dev/null
+++ b/spec/oauth/request_proxy/base_accessors_spec.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "oauth/request_proxy/base"
+
+RSpec.describe OAuth::RequestProxy::Base do
+  # Subclasses that use wrap_values (e.g. ActionControllerRequest,
+  # ActionDispatchRequest) store all parameters as arrays. These specs
+  # verify that every oauth_* accessor safely unwraps array values so
+  # callers always receive a scalar string (or nil), regardless of whether
+  # the parameter arrived as a scalar or a wrapped array.
+  let(:proxy_class) do
+    Class.new(OAuth::RequestProxy::Base) do
+      attr_writer :params
+
+      def parameters
+        @params || {}
+      end
+    end
+  end
+
+  def proxy_with(params)
+    proxy_class.new(Object.new).tap { |p| p.params = params }
+  end
+
+  shared_examples "scalar accessor" do |method, key|
+    it "returns a scalar when the parameter is stored as a single-element array" do
+      p = proxy_with(key => ["value"])
+      expect(p.public_send(method)).to eq("value")
+    end
+
+    it "returns a scalar when the parameter is stored as a plain string" do
+      p = proxy_with(key => "value")
+      expect(p.public_send(method)).to eq("value")
+    end
+
+    it "returns nil when the parameter is absent" do
+      p = proxy_with({})
+      expect(p.public_send(method)).to be_nil
+    end
+  end
+
+  include_examples "scalar accessor", :oauth_consumer_key,    "oauth_consumer_key"
+  include_examples "scalar accessor", :oauth_nonce,           "oauth_nonce"
+  include_examples "scalar accessor", :oauth_timestamp,       "oauth_timestamp"
+  include_examples "scalar accessor", :oauth_token,           "oauth_token"
+  include_examples "scalar accessor", :oauth_signature_method,"oauth_signature_method"
+  include_examples "scalar accessor", :oauth_callback,        "oauth_callback"
+  include_examples "scalar accessor", :oauth_verifier,        "oauth_verifier"
+  include_examples "scalar accessor", :oauth_version,         "oauth_version"
+
+  describe "#oauth_signature" do
+    it "returns a scalar when the parameter is stored as a single-element array" do
+      p = proxy_with("oauth_signature" => ["sig"])
+      expect(p.oauth_signature).to eq("sig")
+    end
+
+    it "returns a scalar when the parameter is stored as a plain string" do
+      p = proxy_with("oauth_signature" => "sig")
+      expect(p.oauth_signature).to eq("sig")
+    end
+
+    it "returns an empty string when the parameter is absent" do
+      p = proxy_with({})
+      expect(p.oauth_signature).to eq("")
+    end
+  end
+end
diff --git a/spec/oauth/request_proxy/rack_spec.rb b/spec/oauth/request_proxy/rack_spec.rb
index 26ef2cf4..81009318 100644
--- a/spec/oauth/request_proxy/rack_spec.rb
+++ b/spec/oauth/request_proxy/rack_spec.rb
@@ -23,6 +23,23 @@ def app
       expect(proxy.parameters).to include("a" => "1", "b" => "2")
     end
 
+    describe "#signature" do
+      it "returns a scalar when oauth_signature is a plain string" do
+        proxy = OAuth::RequestProxy::RackRequest.new(Object.new, clobber_request: true, parameters: {"oauth_signature" => "sig"})
+        expect(proxy.signature).to eq("sig")
+      end
+
+      it "returns a scalar when oauth_signature is a single-element array" do
+        proxy = OAuth::RequestProxy::RackRequest.new(Object.new, clobber_request: true, parameters: {"oauth_signature" => ["sig"]})
+        expect(proxy.signature).to eq("sig")
+      end
+
+      it "returns an empty string when oauth_signature is absent" do
+        proxy = OAuth::RequestProxy::RackRequest.new(Object.new, clobber_request: true, parameters: {})
+        expect(proxy.signature).to eq("")
+      end
+    end
+
     it "proxies Rack::Request POST form params" do
       post "/test", {"x" => "9", "y" => "10"}
       rack_req = last_request