diff --git a/Sources/LightstreamerClient/utils/LsRequestBuilder.swift b/Sources/LightstreamerClient/utils/LsRequestBuilder.swift
index 54d2fb8..97d3976 100644
--- a/Sources/LightstreamerClient/utils/LsRequestBuilder.swift
+++ b/Sources/LightstreamerClient/utils/LsRequestBuilder.swift
@@ -223,6 +223,6 @@ class LsRequestBuilder: CustomStringConvertible {
     var encodedString: String {
         var components = URLComponents()
         components.queryItems = params
-        return components.percentEncodedQuery ?? ""
+        return components.percentEncodedQuery?.replacingOccurrences(of: "+", with: "%2B") ?? ""
     }
 }
diff --git a/Tests/LightstreamerClientTests/LsRequestBuilderTests.swift b/Tests/LightstreamerClientTests/LsRequestBuilderTests.swift
index 0661b65..b016b19 100644
--- a/Tests/LightstreamerClientTests/LsRequestBuilderTests.swift
+++ b/Tests/LightstreamerClientTests/LsRequestBuilderTests.swift
@@ -7,6 +7,6 @@ final class LsRequestBuilderTests: XCTestCase {
         let req = LsRequestBuilder()
         req.addParam("a", "f&=o")
         req.addParam("b", "b +r")
-        XCTAssertEqual("a=f%26%3Do&b=b%20+r", req.encodedString)
+        XCTAssertEqual("a=f%26%3Do&b=b%20%2Br", req.encodedString)
     }
 }
diff --git a/Tests/LightstreamerClientTests/SubscriptionWSTests.swift b/Tests/LightstreamerClientTests/SubscriptionWSTests.swift
index 2135db4..22f3174 100644
--- a/Tests/LightstreamerClientTests/SubscriptionWSTests.swift
+++ b/Tests/LightstreamerClientTests/SubscriptionWSTests.swift
@@ -30,6 +30,33 @@ final class SubscriptionWSTests: BaseTestCase {
                 """, self.io.trace)
         }
     }
+  
+  func testSubscribeFieldWithPlus() {
+      client = newClient("http://server")
+      client.addDelegate(delegate)
+      client.connect()
+      
+      let sub = Subscription(subscriptionMode: .RAW, item: "item", fields: ["f1+f2"])
+      sub.addDelegate(subDelegate)
+      client.subscribe(sub)
+      
+      ws.onOpen()
+      ws.onText("WSOK")
+      ws.onText("CONOK,sid,70000,5000,*")
+      
+      asyncAssert {
+          XCTAssertEqual("""
+              ws.init http://server/lightstreamer
+              wsok
+              create_session\r
+              LS_cid=\(LS_TEST_CID)&LS_send_sync=false&LS_cause=api
+              WSOK
+              CONOK,sid,70000,5000,*
+              control\r
+              LS_reqId=1&LS_op=add&LS_subId=1&LS_mode=RAW&LS_group=item&LS_schema=f1%2Bf2&LS_ack=false
+              """, self.io.trace)
+      }
+  }
     
     func testSubscribe_adapter_schema_group_selector_buffer() {
         client = newClient("http://server")