diff --git a/src/Input/FGButton.cxx b/src/Input/FGButton.cxx
index 400de289e..677f18071 100644
--- a/src/Input/FGButton.cxx
+++ b/src/Input/FGButton.cxx
@@ -46,7 +46,8 @@ FGButton::~FGButton ()
 }
 
 
-void FGButton::init( const SGPropertyNode * node, const std::string & name, std::string & module )
+void FGButton::init(const SGPropertyNode* node, const std::string& name,
+                    const std::string& module)
 {
   if (node == 0) {
     SG_LOG(SG_INPUT, SG_DEBUG, "No bindings for button " << name);
diff --git a/src/Input/FGButton.hxx b/src/Input/FGButton.hxx
index 497be1c46..b002d6446 100644
--- a/src/Input/FGButton.hxx
+++ b/src/Input/FGButton.hxx
@@ -32,7 +32,8 @@ class FGButton : public FGCommonInput {
 public:
   FGButton();
   virtual ~FGButton();
-  void init( const SGPropertyNode * node, const std::string & name, std::string & module );
+  void init(const SGPropertyNode* node, const std::string& name,
+            const std::string& module);
   void update( int modifiers, bool pressed, int x = -1, int y = -1);
   bool is_repeatable;
   float interval_sec, delay_sec, release_delay_sec;