diff --git a/include/GLFW/glfw3.h b/include/GLFW/glfw3.h
index 79b06288..5fbaf1b4 100644
--- a/include/GLFW/glfw3.h
+++ b/include/GLFW/glfw3.h
@@ -1102,6 +1102,7 @@ extern "C" {
  *  [window hint](@ref GLFW_SCALE_FRAMEBUFFER_hint).
  */
 #define GLFW_SCALE_FRAMEBUFFER      0x0002200D
+#define GLFW_FULLSCREEN             0x0002200E
 /*! @brief Legacy name for compatibility.
  *
  *  This is an alias for the
diff --git a/src/cocoa_init.m b/src/cocoa_init.m
index 15dc4ec4..f1e0bad4 100644
--- a/src/cocoa_init.m
+++ b/src/cocoa_init.m
@@ -555,6 +555,7 @@ GLFWbool _glfwConnectCocoa(int platformID, _GLFWplatform* platform)
         .setWindowFloating = _glfwSetWindowFloatingCocoa,
         .setWindowOpacity = _glfwSetWindowOpacityCocoa,
         .setWindowMousePassthrough = _glfwSetWindowMousePassthroughCocoa,
+        .getWindowIsFullscreen = _glfwGetWindowIsFullscreenNull,
         .pollEvents = _glfwPollEventsCocoa,
         .waitEvents = _glfwWaitEventsCocoa,
         .waitEventsTimeout = _glfwWaitEventsTimeoutCocoa,
diff --git a/src/cocoa_platform.h b/src/cocoa_platform.h
index 4d1d66ae..46d81607 100644
--- a/src/cocoa_platform.h
+++ b/src/cocoa_platform.h
@@ -247,6 +247,7 @@ void _glfwSetWindowFloatingCocoa(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityCocoa(_GLFWwindow* window);
 void _glfwSetWindowOpacityCocoa(_GLFWwindow* window, float opacity);
 void _glfwSetWindowMousePassthroughCocoa(_GLFWwindow* window, GLFWbool enabled);
+GLFWbool _glfwGetWindowIsFullscreenCocoa(_GLFWwindow* window);
 
 void _glfwSetRawMouseMotionCocoa(_GLFWwindow *window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedCocoa(void);
diff --git a/src/internal.h b/src/internal.h
index 4f097aa8..d9c555db 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -747,6 +747,7 @@ struct _GLFWplatform
     void (*setWindowFloating)(_GLFWwindow*,GLFWbool);
     void (*setWindowOpacity)(_GLFWwindow*,float);
     void (*setWindowMousePassthrough)(_GLFWwindow*,GLFWbool);
+    GLFWbool (*getWindowIsFullscreen) (_GLFWwindow*);
     void (*pollEvents)(void);
     void (*waitEvents)(void);
     void (*waitEventsTimeout)(double);
diff --git a/src/null_platform.h b/src/null_platform.h
index dbcb835b..88460942 100644
--- a/src/null_platform.h
+++ b/src/null_platform.h
@@ -243,6 +243,8 @@ void _glfwSetWindowResizableNull(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowDecoratedNull(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowFloatingNull(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowMousePassthroughNull(_GLFWwindow* window, GLFWbool enabled);
+GLFWbool _glfwGetWindowIsFullscreenNull(_GLFWwindow* window);
+
 float _glfwGetWindowOpacityNull(_GLFWwindow* window);
 void _glfwSetWindowOpacityNull(_GLFWwindow* window, float opacity);
 void _glfwSetRawMouseMotionNull(_GLFWwindow *window, GLFWbool enabled);
diff --git a/src/null_window.c b/src/null_window.c
index f0e1dcc9..ff3cdce3 100644
--- a/src/null_window.c
+++ b/src/null_window.c
@@ -408,6 +408,11 @@ void _glfwSetWindowMousePassthroughNull(_GLFWwindow* window, GLFWbool enabled)
 {
 }
 
+GLFWbool _glfwGetWindowIsFullscreenNull(_GLFWwindow* window)
+{
+    return 0;
+}
+
 float _glfwGetWindowOpacityNull(_GLFWwindow* window)
 {
     return window->null.opacity;
diff --git a/src/win32_init.c b/src/win32_init.c
index 77ab56ba..a30ebb18 100644
--- a/src/win32_init.c
+++ b/src/win32_init.c
@@ -664,6 +664,7 @@ GLFWbool _glfwConnectWin32(int platformID, _GLFWplatform* platform)
         .setWindowFloating = _glfwSetWindowFloatingWin32,
         .setWindowOpacity = _glfwSetWindowOpacityWin32,
         .setWindowMousePassthrough = _glfwSetWindowMousePassthroughWin32,
+        .getWindowIsFullscreen = _glfwGetWindowIsFullscreenNull,
         .pollEvents = _glfwPollEventsWin32,
         .waitEvents = _glfwWaitEventsWin32,
         .waitEventsTimeout = _glfwWaitEventsTimeoutWin32,
diff --git a/src/win32_platform.h b/src/win32_platform.h
index a2f86852..f2381a81 100644
--- a/src/win32_platform.h
+++ b/src/win32_platform.h
@@ -573,6 +573,7 @@ void _glfwSetWindowResizableWin32(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowDecoratedWin32(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowFloatingWin32(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowMousePassthroughWin32(_GLFWwindow* window, GLFWbool enabled);
+GLFWbool _glfwGetWindowIsFullscreenWin32(_GLFWwindow* window);
 float _glfwGetWindowOpacityWin32(_GLFWwindow* window);
 void _glfwSetWindowOpacityWin32(_GLFWwindow* window, float opacity);
 
diff --git a/src/window.c b/src/window.c
index e03121a4..52536d9f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -900,6 +900,8 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
             return window->focusOnShow;
         case GLFW_MOUSE_PASSTHROUGH:
             return window->mousePassthrough;
+        case GLFW_FULLSCREEN:
+            return _glfw.platform.getWindowIsFullscreen(window);
         case GLFW_TRANSPARENT_FRAMEBUFFER:
             return _glfw.platform.framebufferTransparent(window);
         case GLFW_RESIZABLE:
diff --git a/src/wl_init.c b/src/wl_init.c
index ef9e4503..859cf29f 100644
--- a/src/wl_init.c
+++ b/src/wl_init.c
@@ -506,6 +506,7 @@ GLFWbool _glfwConnectWayland(int platformID, _GLFWplatform* platform)
         .setWindowFloating = _glfwSetWindowFloatingWayland,
         .setWindowOpacity = _glfwSetWindowOpacityWayland,
         .setWindowMousePassthrough = _glfwSetWindowMousePassthroughWayland,
+        .getWindowIsFullscreen = _glfwGetWindowIsFullscreenNull,
         .pollEvents = _glfwPollEventsWayland,
         .waitEvents = _glfwWaitEventsWayland,
         .waitEventsTimeout = _glfwWaitEventsTimeoutWayland,
diff --git a/src/wl_platform.h b/src/wl_platform.h
index afa6f50a..3202e8ff 100644
--- a/src/wl_platform.h
+++ b/src/wl_platform.h
@@ -648,6 +648,7 @@ void _glfwSetWindowFloatingWayland(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityWayland(_GLFWwindow* window);
 void _glfwSetWindowOpacityWayland(_GLFWwindow* window, float opacity);
 void _glfwSetWindowMousePassthroughWayland(_GLFWwindow* window, GLFWbool enabled);
+GLFWbool _glfwGetWindowIsFullscreenWayland(_GLFWwindow* window);
 
 void _glfwSetRawMouseMotionWayland(_GLFWwindow* window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedWayland(void);
diff --git a/src/x11_init.c b/src/x11_init.c
index 6b34c263..1f7c4776 100644
--- a/src/x11_init.c
+++ b/src/x11_init.c
@@ -1237,6 +1237,7 @@ GLFWbool _glfwConnectX11(int platformID, _GLFWplatform* platform)
         .setWindowFloating = _glfwSetWindowFloatingX11,
         .setWindowOpacity = _glfwSetWindowOpacityX11,
         .setWindowMousePassthrough = _glfwSetWindowMousePassthroughX11,
+        .getWindowIsFullscreen = _glfwGetWindowIsFullscreenX11,
         .pollEvents = _glfwPollEventsX11,
         .waitEvents = _glfwWaitEventsX11,
         .waitEventsTimeout = _glfwWaitEventsTimeoutX11,
diff --git a/src/x11_platform.h b/src/x11_platform.h
index 30326c5b..1a918794 100644
--- a/src/x11_platform.h
+++ b/src/x11_platform.h
@@ -934,6 +934,7 @@ void _glfwSetWindowFloatingX11(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityX11(_GLFWwindow* window);
 void _glfwSetWindowOpacityX11(_GLFWwindow* window, float opacity);
 void _glfwSetWindowMousePassthroughX11(_GLFWwindow* window, GLFWbool enabled);
+GLFWbool _glfwGetWindowIsFullscreenX11(_GLFWwindow* window);
 
 void _glfwSetRawMouseMotionX11(_GLFWwindow *window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedX11(void);
diff --git a/src/x11_window.c b/src/x11_window.c
index 322349f0..22aa8548 100644
--- a/src/x11_window.c
+++ b/src/x11_window.c
@@ -2729,6 +2729,51 @@ void _glfwSetWindowMousePassthroughX11(_GLFWwindow* window, GLFWbool enabled)
     }
 }
 
+GLFWbool _glfwGetWindowIsFullscreenX11(_GLFWwindow* window)
+{
+    Atom wm_state = XInternAtom(_glfw.x11.display, "_NET_WM_STATE", True);
+    Atom wm_state_fullscreen = XInternAtom(_glfw.x11.display, "_NET_WM_STATE_FULLSCREEN", True);
+
+    Atom type = XA_ATOM;
+    int format;
+    size_t nItems;
+    size_t bytesAfterReturn;
+    Atom* prop;
+    
+    int result = XGetWindowProperty(
+        _glfw.x11.display,
+        window->x11.handle,
+        wm_state, 
+        0,
+        ~0L,
+        False,
+        AnyPropertyType,
+        &type,
+        &format,
+        &nItems,
+        &bytesAfterReturn,
+        (unsigned char**)&prop 
+    );
+
+    assert(result == Success);
+    assert(nItems > 0);
+
+    if (!prop) {
+        return 0;
+    }
+
+    GLFWbool isFullscreen = 0;
+    for (int i = 0; i < nItems; i++) {
+        if (prop[i] == wm_state_fullscreen) {
+            isFullscreen = 1;
+        }
+    }
+
+    XFree(prop);
+    
+    return isFullscreen;
+}
+
 float _glfwGetWindowOpacityX11(_GLFWwindow* window)
 {
     float opacity = 1.f;
diff --git a/tests/window.c b/tests/window.c
index ffea5dbf..d67e10fc 100644
--- a/tests/window.c
+++ b/tests/window.c
@@ -441,6 +441,7 @@ int main(int argc, char** argv)
             nk_value_bool(nk, "Visible", glfwGetWindowAttrib(window, GLFW_VISIBLE));
             nk_value_bool(nk, "Iconified", glfwGetWindowAttrib(window, GLFW_ICONIFIED));
             nk_value_bool(nk, "Maximized", glfwGetWindowAttrib(window, GLFW_MAXIMIZED));
+            nk_value_bool(nk, "Fullscreen", glfwGetWindowAttrib(window, GLFW_FULLSCREEN));
         }
         nk_end(nk);