diff --git a/src/cocoa_init.m b/src/cocoa_init.m
index 64c99b7c..3d3245f5 100644
--- a/src/cocoa_init.m
+++ b/src/cocoa_init.m
@@ -704,7 +704,8 @@ void _glfwTerminateCocoa(void)
 
 GLFWtheme* _glfwGetSystemDefaultThemeCocoa(void)
 {
-    return NULL;
+    _glfwInputError(GLFW_FEATURE_UNIMPLEMENTED, NULL);
+    return NULL; // TODO: implement
 }
 
 #endif // _GLFW_COCOA
diff --git a/src/cocoa_window.m b/src/cocoa_window.m
index 8391884a..76aac5b2 100644
--- a/src/cocoa_window.m
+++ b/src/cocoa_window.m
@@ -1883,6 +1883,7 @@ void _glfwSetThemeCocoa(_GLFWwindow* window, GLFWtheme* theme)
         [window->ns.object setAppearance:nil];
         return;
     }
+    // TODO: support color
     
     NSAppearanceName name;
     
@@ -1929,6 +1930,8 @@ void _glfwSetThemeCocoa(_GLFWwindow* window, GLFWtheme* theme)
 
 GLFWtheme* _glfwGetThemeCocoa(_GLFWwindow* window)
 {
+    _glfwInputError(GLFW_FEATURE_UNIMPLEMENTED, NULL); // TODO: remove
+    
     GLFWtheme theme;
     NSAppearanceName name = [window->ns.object appearance].name;
     
@@ -1972,7 +1975,7 @@ GLFWtheme* _glfwGetThemeCocoa(_GLFWwindow* window)
     }
     
     //return theme;
-    return NULL;
+    return NULL; // TODO: implement
 }
 
 
diff --git a/src/init.c b/src/init.c
index 890af4aa..52c708eb 100644
--- a/src/init.c
+++ b/src/init.c
@@ -555,5 +555,7 @@ GLFWAPI GLFWthemefun glfwSetSystemThemeCallback(GLFWthemefun callback)
     _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
     
     //return _glfw.platform.setSystemThemeCallback(callback);
-    return NULL;
+    
+    _glfwInputError(GLFW_FEATURE_UNIMPLEMENTED, NULL);
+    return NULL; // TODO: implement
 }
diff --git a/src/null_init.c b/src/null_init.c
index de4b28f3..f42f70b4 100644
--- a/src/null_init.c
+++ b/src/null_init.c
@@ -41,8 +41,11 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
     const _GLFWplatform null =
     {
         GLFW_PLATFORM_NULL,
+        // Init
         _glfwInitNull,
         _glfwTerminateNull,
+        _glfwGetSystemDefaultThemeNull,
+        // Input
         _glfwGetCursorPosNull,
         _glfwSetCursorPosNull,
         _glfwSetCursorModeNull,
@@ -61,6 +64,7 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
         _glfwPollJoystickNull,
         _glfwGetMappingNameNull,
         _glfwUpdateGamepadGUIDNull,
+        // Monitor
         _glfwFreeMonitorNull,
         _glfwGetMonitorPosNull,
         _glfwGetMonitorContentScaleNull,
@@ -69,6 +73,7 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
         _glfwGetVideoModeNull,
         _glfwGetGammaRampNull,
         _glfwSetGammaRampNull,
+        // Window
         _glfwCreateWindowNull,
         _glfwDestroyWindowNull,
         _glfwSetWindowTitleNull,
@@ -102,13 +107,17 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
         _glfwSetWindowFloatingNull,
         _glfwSetWindowOpacityNull,
         _glfwSetWindowMousePassthroughNull,
+        _glfwGetThemeNull,
+        _glfwSetThemeNull,
         _glfwPollEventsNull,
         _glfwWaitEventsNull,
         _glfwWaitEventsTimeoutNull,
         _glfwPostEmptyEventNull,
+        // EGL
         _glfwGetEGLPlatformNull,
         _glfwGetEGLNativeDisplayNull,
         _glfwGetEGLNativeWindowNull,
+        // Vulkan
         _glfwGetRequiredInstanceExtensionsNull,
         _glfwGetPhysicalDevicePresentationSupportNull,
         _glfwCreateWindowSurfaceNull,
@@ -131,3 +140,7 @@ void _glfwTerminateNull(void)
     _glfwTerminateEGL();
 }
 
+GLFWtheme* _glfwGetSystemDefaultThemeNull(void)
+{
+    return NULL; // TODO: should probably return a colorless GLFWtheme with baseTheme set to GLFW_BASE_THEME_LIGHT
+}
diff --git a/src/null_platform.h b/src/null_platform.h
index b646acb3..44a61cad 100644
--- a/src/null_platform.h
+++ b/src/null_platform.h
@@ -147,3 +147,6 @@ VkResult _glfwCreateWindowSurfaceNull(VkInstance instance, _GLFWwindow* window,
 
 void _glfwPollMonitorsNull(void);
 
+GLFWtheme* _glfwGetSystemDefaultThemeNull(void);
+void _glfwSetThemeNull(_GLFWwindow* window, GLFWtheme* theme);
+GLFWtheme* _glfwGetThemeNull(_GLFWwindow* window);
diff --git a/src/null_window.c b/src/null_window.c
index 5cdf3e23..2804fa59 100644
--- a/src/null_window.c
+++ b/src/null_window.c
@@ -551,6 +551,15 @@ const char* _glfwGetClipboardStringNull(void)
     return _glfw.null.clipboardString;
 }
 
+void _glfwSetThemeNull(_GLFWwindow* window, GLFWtheme* theme)
+{
+}
+
+GLFWtheme* _glfwGetThemeNull(_GLFWwindow* window)
+{
+    return NULL; // TODO: see to-do in _glfwGetSystemDefaultThemeNull
+}
+
 EGLenum _glfwGetEGLPlatformNull(EGLint** attribs)
 {
     return 0;