diff --git a/gtk/gui-thread-check/profiler/gui-thread-check.c b/gtk/gui-thread-check/profiler/gui-thread-check.c
index fecef800a..4ec8643bd 100644
--- a/gtk/gui-thread-check/profiler/gui-thread-check.c
+++ b/gtk/gui-thread-check/profiler/gui-thread-check.c
@@ -23,11 +23,12 @@
  * USA.
  */
 
+#include <string.h>
 #include <glib.h>
 #include <mono/metadata/profiler.h>
 
 
-extern pthread_t pthread_self ();
+extern pthread_t pthread_self (void);
 
 static gboolean
 stack_walk_fn (MonoMethod *method, gint32 native_offset, gint32 il_offset, gboolean managed, gpointer data)