diff --git a/lib/webmock/request_signature.rb b/lib/webmock/request_signature.rb
index 70686f40..949b874a 100644
--- a/lib/webmock/request_signature.rb
+++ b/lib/webmock/request_signature.rb
@@ -35,11 +35,11 @@ def eql?(other)
     alias == eql?
 
     def url_encoded?
-      !!(headers && headers['Content-Type'] == 'application/x-www-form-urlencoded')
+      !!(headers&.fetch('Content-Type', nil)&.start_with?('application/x-www-form-urlencoded'))
     end
 
     def json_headers?
-      !!(headers && headers['Content-Type'] == 'application/json')
+      !!(headers&.fetch('Content-Type', nil)&.start_with?('application/json'))
     end
 
     private
diff --git a/spec/unit/request_signature_spec.rb b/spec/unit/request_signature_spec.rb
index 02a5ec17..a330b57f 100644
--- a/spec/unit/request_signature_spec.rb
+++ b/spec/unit/request_signature_spec.rb
@@ -125,11 +125,21 @@
       expect(subject.url_encoded?).to be true
     end
 
+    it "returns true if the headers are urlencoded with a specified charset" do
+      subject.headers = { "Content-Type" => "application/x-www-form-urlencoded; charset=UTF-8" }
+      expect(subject.url_encoded?).to be true
+    end
+
     it "returns false if the headers are NOT urlencoded" do
       subject.headers = { "Content-Type" => "application/made-up-format" }
       expect(subject.url_encoded?).to be false
     end
 
+    it "returns false when no content type header is present" do
+      subject.headers = { "Some-Header" => "some-value" }
+      expect(subject.url_encoded?).to be false
+    end
+
     it "returns false when no headers are set" do
       subject.headers = nil
       expect(subject.url_encoded?).to be false
@@ -142,11 +152,21 @@
       expect(subject.json_headers?).to be true
     end
 
+    it "returns true if the headers are json with a specified charset" do
+      subject.headers = { "Content-Type" => "application/json; charset=UTF-8" }
+      expect(subject.json_headers?).to be true
+    end
+
     it "returns false if the headers are NOT json" do
       subject.headers = { "Content-Type" => "application/made-up-format" }
       expect(subject.json_headers?).to be false
     end
 
+    it "returns false when no content type header is present" do
+      subject.headers = { "Some-Header" => "some-value" }
+      expect(subject.json_headers?).to be false
+    end
+
     it "returns false when no headers are set" do
       subject.headers = nil
       expect(subject.json_headers?).to be false