diff --git a/imgui.cpp b/imgui.cpp
index 6ce2b950d253..3215b9b0c491 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -4034,7 +4034,7 @@ void ImGui::NewFrame()
     UpdateTabFocus();
 
     // Mark all windows as not visible and compact unused memory.
-    IM_ASSERT(g.WindowsFocusOrder.Size == g.Windows.Size);
+    IM_ASSERT(g.WindowsFocusOrder.Size <= g.Windows.Size);
     const float memory_compact_start_time = (g.GcCompactAll || g.IO.ConfigMemoryCompactTimer < 0.0f) ? FLT_MAX : (float)g.Time - g.IO.ConfigMemoryCompactTimer;
     for (int i = 0; i != g.Windows.Size; i++)
     {
@@ -5143,7 +5143,12 @@ static ImGuiWindow* CreateNewWindow(const char* name, ImGuiWindowFlags flags)
         window->AutoFitOnlyGrows = (window->AutoFitFramesX > 0) || (window->AutoFitFramesY > 0);
     }
 
-    g.WindowsFocusOrder.push_back(window);
+    if (!(flags & ImGuiWindowFlags_ChildWindow))
+    {
+        g.WindowsFocusOrder.push_back(window);
+        window->FocusOrder = (short)(g.WindowsFocusOrder.Size - 1);
+    }
+
     if (flags & ImGuiWindowFlags_NoBringToFrontOnFocus)
         g.Windows.push_front(window); // Quite slow but rare and only once
     else
@@ -6378,15 +6383,22 @@ void ImGui::End()
 void ImGui::BringWindowToFocusFront(ImGuiWindow* window)
 {
     ImGuiContext& g = *GImGui;
+    IM_ASSERT(window == window->RootWindow);
+
+    const int cur_order = window->FocusOrder;
+    IM_ASSERT(g.WindowsFocusOrder[cur_order] == window);
     if (g.WindowsFocusOrder.back() == window)
         return;
-    for (int i = g.WindowsFocusOrder.Size - 2; i >= 0; i--) // We can ignore the top-most window
-        if (g.WindowsFocusOrder[i] == window)
-        {
-            memmove(&g.WindowsFocusOrder[i], &g.WindowsFocusOrder[i + 1], (size_t)(g.WindowsFocusOrder.Size - i - 1) * sizeof(ImGuiWindow*));
-            g.WindowsFocusOrder[g.WindowsFocusOrder.Size - 1] = window;
-            break;
-        }
+
+    const int new_order = g.WindowsFocusOrder.Size - 1;
+    for (int n = cur_order; n < new_order; n++)
+    {
+        g.WindowsFocusOrder[n] = g.WindowsFocusOrder[n + 1];
+        g.WindowsFocusOrder[n]->FocusOrder--;
+        IM_ASSERT(g.WindowsFocusOrder[n]->FocusOrder == n);
+    }
+    g.WindowsFocusOrder[new_order] = window;
+    window->FocusOrder = (short)new_order;
 }
 
 void ImGui::BringWindowToDisplayFront(ImGuiWindow* window)
@@ -6466,18 +6478,13 @@ void ImGui::FocusTopMostWindowUnderOne(ImGuiWindow* under_this_window, ImGuiWind
 {
     ImGuiContext& g = *GImGui;
 
-    int start_idx = g.WindowsFocusOrder.Size - 1;
-    if (under_this_window != NULL)
-    {
-        int under_this_window_idx = FindWindowFocusIndex(under_this_window);
-        if (under_this_window_idx != -1)
-            start_idx = under_this_window_idx - 1;
-    }
+    const int start_idx = ((under_this_window != NULL) ? FindWindowFocusIndex(under_this_window) : g.WindowsFocusOrder.Size) - 1;
     for (int i = start_idx; i >= 0; i--)
     {
         // We may later decide to test for different NoXXXInputs based on the active navigation input (mouse vs nav) but that may feel more confusing to the user.
         ImGuiWindow* window = g.WindowsFocusOrder[i];
-        if (window != ignore_window && window->WasActive && !(window->Flags & ImGuiWindowFlags_ChildWindow))
+        IM_ASSERT(window == window->RootWindow);
+        if (window != ignore_window && window->WasActive)
             if ((window->Flags & (ImGuiWindowFlags_NoMouseInputs | ImGuiWindowFlags_NoNavInputs)) != (ImGuiWindowFlags_NoMouseInputs | ImGuiWindowFlags_NoNavInputs))
             {
                 ImGuiWindow* focus_window = NavRestoreLastChildNavWindow(window);
@@ -9479,13 +9486,12 @@ static void ImGui::NavEndFrame()
     }
 }
 
-static int ImGui::FindWindowFocusIndex(ImGuiWindow* window) // FIXME-OPT O(N)
+static int ImGui::FindWindowFocusIndex(ImGuiWindow* window)
 {
     ImGuiContext& g = *GImGui;
-    for (int i = g.WindowsFocusOrder.Size - 1; i >= 0; i--)
-        if (g.WindowsFocusOrder[i] == window)
-            return i;
-    return -1;
+    int order = window->FocusOrder;
+    IM_ASSERT(g.WindowsFocusOrder[order] == window);
+    return order;
 }
 
 static ImGuiWindow* FindWindowNavFocusable(int i_start, int i_stop, int dir) // FIXME-OPT O(N)
diff --git a/imgui_internal.h b/imgui_internal.h
index c100cfc9f944..a8c2b440ef80 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -1322,7 +1322,7 @@ struct ImGuiContext
 
     // Windows state
     ImVector<ImGuiWindow*>  Windows;                            // Windows, sorted in display order, back to front
-    ImVector<ImGuiWindow*>  WindowsFocusOrder;                  // Windows, sorted in focus order, back to front. (FIXME: We could only store root windows here! Need to sort out the Docking equivalent which is RootWindowDockStop and is unfortunately a little more dynamic)
+    ImVector<ImGuiWindow*>  WindowsFocusOrder;                  // Root windows, sorted in focus order, back to front.
     ImVector<ImGuiWindow*>  WindowsTempSortBuffer;              // Temporary buffer used in EndFrame() to reorder windows so parents are kept before their child
     ImVector<ImGuiWindow*>  CurrentWindowStack;
     ImGuiStorage            WindowsById;                        // Map window's ImGuiID to ImGuiWindow*
@@ -1786,8 +1786,9 @@ struct IMGUI_API ImGuiWindow
     bool                    HasCloseButton;                     // Set when the window has a close button (p_open != NULL)
     signed char             ResizeBorderHeld;                   // Current border being held for resize (-1: none, otherwise 0-3)
     short                   BeginCount;                         // Number of Begin() during the current frame (generally 0 or 1, 1+ if appending via multiple Begin/End pairs)
-    short                   BeginOrderWithinParent;             // Order within immediate parent window, if we are a child window. Otherwise 0.
-    short                   BeginOrderWithinContext;            // Order within entire imgui context. This is mostly used for debugging submission order related issues.
+    short                   BeginOrderWithinParent;             // Begin() order within immediate parent window, if we are a child window. Otherwise 0.
+    short                   BeginOrderWithinContext;            // Begin() order within entire imgui context. This is mostly used for debugging submission order related issues.
+    short                   FocusOrder;                         // Order within WindowsFocusOrder[], altered when windows are focused.
     ImGuiID                 PopupId;                            // ID in the popup stack when this window is used as a popup/menu (because we use generic Name/ID for recycling)
     ImS8                    AutoFitFramesX, AutoFitFramesY;
     ImS8                    AutoFitChildAxises;