diff --git a/include/GL/glfw.h b/include/GL/glfw.h
index 4647b7bf..5f433bc7 100644
--- a/include/GL/glfw.h
+++ b/include/GL/glfw.h
@@ -364,14 +364,14 @@ typedef struct {
 } GLFWvidmode;
 
 /* Function pointer types */
-typedef void (* GLFWwindowsizefun)(int,int);
-typedef int  (* GLFWwindowclosefun)(void);
-typedef void (* GLFWwindowrefreshfun)(void);
-typedef void (* GLFWmousebuttonfun)(int,int);
-typedef void (* GLFWmouseposfun)(int,int);
-typedef void (* GLFWmousewheelfun)(int);
-typedef void (* GLFWkeyfun)(int,int);
-typedef void (* GLFWcharfun)(int,int);
+typedef void (* GLFWwindowsizefun)(GLFWwindow,int,int);
+typedef int  (* GLFWwindowclosefun)(GLFWwindow);
+typedef void (* GLFWwindowrefreshfun)(GLFWwindow);
+typedef void (* GLFWmousebuttonfun)(GLFWwindow,int,int);
+typedef void (* GLFWmouseposfun)(GLFWwindow,int,int);
+typedef void (* GLFWmousewheelfun)(GLFWwindow,int);
+typedef void (* GLFWkeyfun)(GLFWwindow,int,int);
+typedef void (* GLFWcharfun)(GLFWwindow,int,int);
 
 
 /*************************************************************************
diff --git a/lib/enable.c b/lib/enable.c
index e20f8942..a55e785f 100644
--- a/lib/enable.c
+++ b/lib/enable.c
@@ -61,7 +61,8 @@ static void enableMouseCursor(_GLFWwindow* window)
 
         if (window->mousePosCallback)
         {
-            window->mousePosCallback(window->mousePosX,
+            window->mousePosCallback(window,
+                                     window->mousePosX,
                                      window->mousePosY);
         }
     }
diff --git a/lib/input.c b/lib/input.c
index f75ede7b..f004dc9d 100644
--- a/lib/input.c
+++ b/lib/input.c
@@ -203,7 +203,7 @@ GLFWAPI void glfwSetMousePosCallback(GLFWwindow window, GLFWmouseposfun cbfun)
     // Call the callback function to let the application know the current
     // mouse position
     if (cbfun)
-        cbfun(window->mousePosX, window->mousePosY);
+        cbfun(window, window->mousePosX, window->mousePosY);
 }
 
 
@@ -222,6 +222,6 @@ GLFWAPI void glfwSetMouseWheelCallback(GLFWwindow window, GLFWmousewheelfun cbfu
     // Call the callback function to let the application know the current
     // mouse wheel position
     if (cbfun)
-        cbfun(window->wheelPos);
+        cbfun(window, window->wheelPos);
 }
 
diff --git a/lib/window.c b/lib/window.c
index 5383e29f..67f93f1e 100644
--- a/lib/window.c
+++ b/lib/window.c
@@ -141,7 +141,7 @@ void _glfwInputKey(_GLFWwindow* window, int key, int action)
 
     // Call user callback function
     if (window->keyCallback && (window->keyRepeat || !keyrepeat) )
-        window->keyCallback(key, action);
+        window->keyCallback(window, key, action);
 }
 
 
@@ -186,7 +186,7 @@ void _glfwInputChar(_GLFWwindow* window, int character, int action)
     }
 
     if (window->charCallback && (window->keyRepeat || !keyrepeat))
-        window->charCallback(character, action);
+        window->charCallback(window, character, action);
 }
 
 
@@ -206,7 +206,7 @@ void _glfwInputMouseClick(_GLFWwindow* window, int button, int action)
         window->mouseButton[button] = (char) action;
 
     if (window->mouseButtonCallback)
-        window->mouseButtonCallback(button, action);
+        window->mouseButtonCallback(window, button, action);
 }
 
 
@@ -580,9 +580,12 @@ GLFWAPI void glfwMakeWindowCurrent(GLFWwindow window)
 GLFWAPI int glfwIsWindow(GLFWwindow window)
 {
     if (!_glfwInitialized)
-        return;
+        return GL_FALSE;
 
-    return window == _glfwLibrary.window;
+    if (window == NULL)
+        return GL_FALSE;
+
+    return (window == _glfwLibrary.window) ? GL_TRUE : GL_FALSE;
 }
 
 
@@ -873,7 +876,7 @@ GLFWAPI void glfwSetWindowSizeCallback(GLFWwindow window, GLFWwindowsizefun cbfu
     // Call the callback function to let the application know the current
     // window size
     if (cbfun)
-        cbfun(window->width, window->height);
+        cbfun(window, window->width, window->height);
 }
 
 //========================================================================
diff --git a/lib/x11/x11_window.c b/lib/x11/x11_window.c
index 35d1fc44..722939a9 100644
--- a/lib/x11/x11_window.c
+++ b/lib/x11/x11_window.c
@@ -1088,13 +1088,13 @@ static GLboolean processSingleEvent(void)
             {
                 window->wheelPos++;  // To verify: is this up or down?
                 if (window->mouseWheelCallback)
-                    window->mouseWheelCallback(window->wheelPos);
+                    window->mouseWheelCallback(window, window->wheelPos);
             }
             else if (event.xbutton.button == Button5)
             {
                 window->wheelPos--;
                 if (window->mouseWheelCallback)
-                    window->mouseWheelCallback(window->wheelPos);
+                    window->mouseWheelCallback(window, window->wheelPos);
             }
             break;
         }
@@ -1155,7 +1155,8 @@ static GLboolean processSingleEvent(void)
 
                 if (window->mousePosCallback)
                 {
-                    window->mousePosCallback(window->mousePosX,
+                    window->mousePosCallback(window,
+                                             window->mousePosX,
                                              window->mousePosY);
                 }
             }
@@ -1173,7 +1174,8 @@ static GLboolean processSingleEvent(void)
                 window->height = event.xconfigure.height;
                 if (window->windowSizeCallback)
                 {
-                    window->windowSizeCallback(window->width,
+                    window->windowSizeCallback(window,
+                                               window->width,
                                                window->height);
                 }
             }
@@ -1252,7 +1254,7 @@ static GLboolean processSingleEvent(void)
             // The window's contents was damaged
 
             if (window->windowRefreshCallback)
-                window->windowRefreshCallback();
+                window->windowRefreshCallback(window);
 
             break;
         }
@@ -1697,7 +1699,7 @@ void _glfwPlatformPollEvents(void)
     }
 
     if (closeRequested && window->windowCloseCallback)
-        closeRequested = window->windowCloseCallback();
+        closeRequested = window->windowCloseCallback(window);
 
     if (closeRequested)
         glfwCloseWindow(window);