diff --git a/lib/jwt/encode.rb b/lib/jwt/encode.rb
index 2bc23963..b20852eb 100644
--- a/lib/jwt/encode.rb
+++ b/lib/jwt/encode.rb
@@ -27,7 +27,7 @@ def encoded_header(algorithm, header_fields)
     end
 
     def encoded_payload(payload)
-      raise InvalidPayload, 'exp claim must be an integer' if payload && payload['exp'] && payload['exp'].is_a?(Time)
+      raise InvalidPayload, 'exp claim must be an integer' if payload && payload['exp'] && !payload['exp'].is_a?(Integer)
       Encode.base64url_encode(JSON.generate(payload))
     end
 
diff --git a/spec/jwt_spec.rb b/spec/jwt_spec.rb
index 2db731da..62ebf5c5 100644
--- a/spec/jwt_spec.rb
+++ b/spec/jwt_spec.rb
@@ -60,6 +60,14 @@
         JWT.encode payload, nil, alg
       end.to raise_error JWT::InvalidPayload
     end
+
+    it 'should display a better error message if payload exp is not an Integer' do
+      payload['exp'] = Time.now.to_i.to_s
+
+      expect do
+        JWT.encode payload, nil, alg
+      end.to raise_error JWT::InvalidPayload
+    end
   end
 
   %w(HS256 HS512256 HS384 HS512).each do |alg|