diff --git a/hw/dmx/glxProxy/glxscreens.c b/hw/dmx/glxProxy/glxscreens.c
index b62776c41..15bb1e862 100644
--- a/hw/dmx/glxProxy/glxscreens.c
+++ b/hw/dmx/glxProxy/glxscreens.c
@@ -335,7 +335,7 @@ __glXGetServerString(unsigned int name)
 }
 
 int
-glxIsExtensionSupported(char *ext)
+glxIsExtensionSupported(const char *ext)
 {
     return (strstr(ExtensionsString, ext) != NULL);
 }
diff --git a/hw/dmx/glxProxy/glxscreens.h b/hw/dmx/glxProxy/glxscreens.h
index 9a538d193..bb7477bc7 100644
--- a/hw/dmx/glxProxy/glxscreens.h
+++ b/hw/dmx/glxProxy/glxscreens.h
@@ -50,6 +50,6 @@ extern void __glXScreenReset(void);
 
 extern char *__glXGetServerString(unsigned int name);
 
-extern int glxIsExtensionSupported(char *ext);
+extern int glxIsExtensionSupported(const char *ext);
 
 #endif                          /* !__GLX_screens_h__ */