diff --git a/src/gui/doAction.cpp b/src/gui/doAction.cpp
index ff47ac0f3..950815f02 100644
--- a/src/gui/doAction.cpp
+++ b/src/gui/doAction.cpp
@@ -210,6 +210,7 @@ void FurnaceGUI::doAction(int what) {
       followPattern=!followPattern;
       break;
     case GUI_ACTION_FULLSCREEN:
+      if (sysFullScreen) break;
       fullScreen=!fullScreen;
       SDL_SetWindowFullscreen(sdlWin,fullScreen?(SDL_WINDOW_FULLSCREEN|SDL_WINDOW_FULLSCREEN_DESKTOP):0);
       break;
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 3c0c9a7f8..03422f538 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -3987,7 +3987,7 @@ bool FurnaceGUI::loop() {
           break;
         case SDL_WINDOWEVENT:
           switch (ev.window.event) {
-            case SDL_WINDOWEVENT_RESIZED:
+            case SDL_WINDOWEVENT_RESIZED: {
               scrW=ev.window.data1;
               scrH=ev.window.data2;
               portrait=(scrW<scrH);
@@ -3995,7 +3995,32 @@ bool FurnaceGUI::loop() {
               logD("window resized to %dx%d",scrW,scrH);
               updateWindow=true;
               rend->resized(ev);
+
+              // check whether we're in fullscreen
+              int displayOfWindow=SDL_GetWindowDisplayIndex(sdlWin);
+              SDL_Rect displayRect;
+              if (displayOfWindow<0) {
+                logW("couldn't get display of window after resize! (%s)",SDL_GetError());
+                break;
+              }
+
+              if (SDL_GetDisplayBounds(displayOfWindow,&displayRect)!=0) {
+                logW("couldn't get display bounds after resize! (%s)",SDL_GetError());
+                break;
+              }
+
+              if (fullScreen) {
+                sysFullScreen=false;
+              } else {
+                if (scrW==displayRect.w && scrH==displayRect.h) {
+                  logD("we may be in fullscreen");
+                  sysFullScreen=true;
+                } else {
+                  sysFullScreen=false;
+                }
+              }
               break;
+            }
             case SDL_WINDOWEVENT_MOVED:
               scrX=ev.window.data1;
               scrY=ev.window.data2;
@@ -4160,7 +4185,7 @@ bool FurnaceGUI::loop() {
     // update config x/y/w/h values based on scrMax state
     if (updateWindow) {
       logV("updateWindow is true");
-      if (!scrMax && !fullScreen) {
+      if (!scrMax && !fullScreen && !sysFullScreen) {
         logV("updating scrConf");
         scrConfX=scrX;
         scrConfY=scrY;
@@ -4829,9 +4854,14 @@ bool FurnaceGUI::loop() {
       }
       if (ImGui::BeginMenu(settings.capitalMenuBar?_("Settings"):_("settings"))) {
 #ifndef IS_MOBILE
-        if (ImGui::MenuItem(_("full screen"),BIND_FOR(GUI_ACTION_FULLSCREEN),fullScreen)) {
+        ImGui::BeginDisabled(sysFullScreen);
+        if (ImGui::MenuItem(_("full screen"),BIND_FOR(GUI_ACTION_FULLSCREEN),fullScreen || sysFullScreen)) {
           doAction(GUI_ACTION_FULLSCREEN);
         }
+        ImGui::EndDisabled();
+        if (sysFullScreen) {
+          ImGui::SetItemTooltip(_("the system has set Furnace to full screen."));
+        }
 #endif
         if (ImGui::MenuItem(_("lock layout"),NULL,lockLayout)) {
           lockLayout=!lockLayout;
@@ -8773,6 +8803,7 @@ FurnaceGUI::FurnaceGUI():
   displayNew(false),
   displayPalette(false),
   fullScreen(false),
+  sysFullScreen(false),
   preserveChanPos(false),
   sysDupCloneChannels(true),
   sysDupEnd(false),
diff --git a/src/gui/gui.h b/src/gui/gui.h
index a475dd6dd..c462c6790 100644
--- a/src/gui/gui.h
+++ b/src/gui/gui.h
@@ -1740,7 +1740,7 @@ class FurnaceGUI {
   bool vgmExportDirectStream, displayInsTypeList, displayWaveSizeList;
   bool portrait, injectBackUp, mobileMenuOpen, warnColorPushed;
   bool wantCaptureKeyboard, oldWantCaptureKeyboard, displayMacroMenu;
-  bool displayNew, displayExport, displayPalette, fullScreen, preserveChanPos, sysDupCloneChannels, sysDupEnd;
+  bool displayNew, displayExport, displayPalette, fullScreen, sysFullScreen, preserveChanPos, sysDupCloneChannels, sysDupEnd;
   unsigned char noteInputMode;
   bool notifyWaveChange, notifySampleChange;
   bool recalcTimestamps;