diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 56686f233..6803d9a7c 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -43,6 +43,7 @@ Other Changes:
 - Scrolling: Fix scroll snapping on edge of scroll region when both scrollbars are enabled.
 - Scrolling: Fix mouse wheel axis swap when using SHIFT on macOS (system already does it). (#4010)
 - Window: Fix IsWindowAppearing() from returning true twice in most cases. (#3982, #1497, #1061)
+- Nav: Fixed using SetItemDefaultFocus() on windows with _NavFlattened flag.
 - Tables: Expose TableSetColumnEnabled() in public api. (#3935)
 - Tables: Better preserve widths when columns count changes. (#4046)
 - TabBar: Fixed mouse reordering with very fast movements (e.g. crossing multiple tabs in a single
diff --git a/imgui.cpp b/imgui.cpp
index 3215b9b0c..7b8ac8667 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -6977,11 +6977,11 @@ void ImGui::SetItemDefaultFocus()
     ImGuiWindow* window = g.CurrentWindow;
     if (!window->Appearing)
         return;
-    if (g.NavWindow == window->RootWindowForNav && (g.NavInitRequest || g.NavInitResultId != 0) && g.NavLayer == g.NavWindow->DC.NavLayerCurrent)
+    if (g.NavWindow == window->RootWindowForNav && (g.NavInitRequest || g.NavInitResultId != 0) && g.NavLayer == window->DC.NavLayerCurrent)
     {
         g.NavInitRequest = false;
-        g.NavInitResultId = g.NavWindow->DC.LastItemId;
-        g.NavInitResultRectRel = ImRect(g.NavWindow->DC.LastItemRect.Min - g.NavWindow->Pos, g.NavWindow->DC.LastItemRect.Max - g.NavWindow->Pos);
+        g.NavInitResultId = window->DC.LastItemId;
+        g.NavInitResultRectRel = ImRect(window->DC.LastItemRect.Min - window->Pos, window->DC.LastItemRect.Max - window->Pos);
         NavUpdateAnyRequestFlag();
         if (!IsItemVisible())
             SetScrollHereY();
@@ -9276,6 +9276,7 @@ static void ImGui::NavUpdateInitResult()
         return;
 
     // Apply result from previous navigation init request (will typically select the first item, unless SetItemDefaultFocus() has been called)
+    // FIXME-NAV: On _NavFlattened windows, g.NavWindow will only be updated during subsequent frame. Not a problem currently.
     IMGUI_DEBUG_LOG_NAV("[nav] NavInitRequest: result NavID 0x%08X in Layer %d Window \"%s\"\n", g.NavInitResultId, g.NavLayer, g.NavWindow->Name);
     SetNavID(g.NavInitResultId, g.NavLayer, 0, g.NavInitResultRectRel);
     if (g.NavInitRequestFromMove)
@@ -9630,7 +9631,8 @@ static void ImGui::NavUpdateWindowing()
         if (apply_focus_window->NavLastIds[0] == 0)
             NavInitWindow(apply_focus_window, false);
 
-        // If the window only has a menu layer, select it directly
+        // If the window has ONLY a menu layer (no main layer), select it directly
+        // FIXME-NAV: This should be done in NavInit.. or in FocusWindow..
         if (apply_focus_window->DC.NavLayerActiveMask == (1 << ImGuiNavLayer_Menu))
             g.NavLayer = ImGuiNavLayer_Menu;
     }
@@ -11465,12 +11467,19 @@ void ImGui::DebugNodeWindow(ImGuiWindow* window, const char* label)
     BulletText("Scroll: (%.2f/%.2f,%.2f/%.2f) Scrollbar:%s%s", window->Scroll.x, window->ScrollMax.x, window->Scroll.y, window->ScrollMax.y, window->ScrollbarX ? "X" : "", window->ScrollbarY ? "Y" : "");
     BulletText("Active: %d/%d, WriteAccessed: %d, BeginOrderWithinContext: %d", window->Active, window->WasActive, window->WriteAccessed, (window->Active || window->WasActive) ? window->BeginOrderWithinContext : -1);
     BulletText("Appearing: %d, Hidden: %d (CanSkip %d Cannot %d), SkipItems: %d", window->Appearing, window->Hidden, window->HiddenFramesCanSkipItems, window->HiddenFramesCannotSkipItems, window->SkipItems);
-    BulletText("NavLastIds: 0x%08X,0x%08X, NavLayerActiveMask: %X", window->NavLastIds[0], window->NavLastIds[1], window->DC.NavLayerActiveMask);
-    BulletText("NavLastChildNavWindow: %s", window->NavLastChildNavWindow ? window->NavLastChildNavWindow->Name : "NULL");
-    if (!window->NavRectRel[0].IsInverted())
-        BulletText("NavRectRel[0]: (%.1f,%.1f)(%.1f,%.1f)", window->NavRectRel[0].Min.x, window->NavRectRel[0].Min.y, window->NavRectRel[0].Max.x, window->NavRectRel[0].Max.y);
-    else
-        BulletText("NavRectRel[0]: <None>");
+    for (int layer = 0; layer < ImGuiNavLayer_COUNT; layer++)
+    {
+        ImRect r = window->NavRectRel[layer];
+        if (r.Min.x >= r.Max.y && r.Min.y >= r.Max.y)
+        {
+            BulletText("NavLastIds[%d]: 0x%08X", layer, window->NavLastIds[layer]);
+            continue;
+        }
+        BulletText("NavLastIds[%d]: 0x%08X at +(%.1f,%.1f)(%.1f,%.1f)", layer, window->NavLastIds[layer], r.Min.x, r.Min.y, r.Max.x, r.Max.y);
+        if (IsItemHovered())
+            GetForegroundDrawList(window)->AddRect(r.Min + window->Pos, r.Max + window->Pos, IM_COL32(255, 255, 0, 255));
+    }
+    BulletText("NavLayerActiveMask: %X, NavLastChildNavWindow: %s", window->DC.NavLayerActiveMask, window->NavLastChildNavWindow ? window->NavLastChildNavWindow->Name : "NULL");
     if (window->RootWindow != window)       { DebugNodeWindow(window->RootWindow, "RootWindow"); }
     if (window->ParentWindow != NULL)       { DebugNodeWindow(window->ParentWindow, "ParentWindow"); }
     if (window->DC.ChildWindows.Size > 0)   { DebugNodeWindowsList(&window->DC.ChildWindows, "ChildWindows"); }
diff --git a/imgui.h b/imgui.h
index 44b9922a3..ee36cfd65 100644
--- a/imgui.h
+++ b/imgui.h
@@ -61,7 +61,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.83 WIP"
-#define IMGUI_VERSION_NUM           18204
+#define IMGUI_VERSION_NUM           18205
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE