diff --git a/src/libs/languageserverprotocol/messages.cpp b/src/libs/languageserverprotocol/messages.cpp
index 310dd88ebea..6e02e5180e3 100644
--- a/src/libs/languageserverprotocol/messages.cpp
+++ b/src/libs/languageserverprotocol/messages.cpp
@@ -67,7 +67,7 @@ static QString messageTypeName(int messageType)
     return QString("");
 }
 
-QString ShowMessageParams::toString()
+QString ShowMessageParams::toString() const
 {
     return messageTypeName(type()) + ": " + message();
 }
diff --git a/src/libs/languageserverprotocol/messages.h b/src/libs/languageserverprotocol/messages.h
index a5ddf5df90b..ff807a93726 100644
--- a/src/libs/languageserverprotocol/messages.h
+++ b/src/libs/languageserverprotocol/messages.h
@@ -47,7 +47,7 @@ public:
     QString message() const { return typedValue<QString>(messageKey); }
     void setMessage(QString message) { insert(messageKey, message); }
 
-    QString toString();
+    QString toString() const;
 
     bool isValid(QStringList *error) const override
     { return check<int>(error, typeKey) && check<QString>(error, messageKey); }
diff --git a/src/plugins/languageclient/baseclient.cpp b/src/plugins/languageclient/baseclient.cpp
index f46150e792e..dac8e88be6b 100644
--- a/src/plugins/languageclient/baseclient.cpp
+++ b/src/plugins/languageclient/baseclient.cpp
@@ -516,7 +516,8 @@ void BaseClient::log(const QString &message, Core::MessageManager::PrintToOutput
     Core::MessageManager::write(QString("LanguageClient %1: %2").arg(name(), message), flag);
 }
 
-void BaseClient::log(LogMessageParams &message, Core::MessageManager::PrintToOutputPaneFlag flag)
+void BaseClient::log(const LogMessageParams &message,
+                     Core::MessageManager::PrintToOutputPaneFlag flag)
 {
     log(message.toString(), flag);
 }
diff --git a/src/plugins/languageclient/baseclient.h b/src/plugins/languageclient/baseclient.h
index 4bd733dfdd8..5c4ba6ed25c 100644
--- a/src/plugins/languageclient/baseclient.h
+++ b/src/plugins/languageclient/baseclient.h
@@ -118,7 +118,7 @@ public:
 
     void log(const QString &message,
              Core::MessageManager::PrintToOutputPaneFlag flag = Core::MessageManager::NoModeSwitch);
-    void log(LanguageServerProtocol::LogMessageParams &message,
+    void log(const LanguageServerProtocol::LogMessageParams &message,
              Core::MessageManager::PrintToOutputPaneFlag flag = Core::MessageManager::NoModeSwitch);
 
 signals: