diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index fb0059a41e13..3ab3774ce182 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -154,6 +154,9 @@ Other Changes:
 
 Docking+Viewports Branch:
 
+- Viewports: Made it possible to explicitly assign ImGuiWindowClass::ParentViewportId to 0 in order
+  to ensure a window is not parented. Previously this would use the global default (which might be 0,
+  but not always as it would depend on io.ConfigViewportsNoDefaultParent). (#3152, #2871)
 - Disabled: Fixed nested BeginDisabled()/EndDisabled() bug in Docking branch due to bad merge. (#4655, #4452, #4453, #4462)
 
 
diff --git a/imgui.cpp b/imgui.cpp
index ace13208ffe1..730a6a8758d5 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -12457,7 +12457,7 @@ void ImGui::WindowSyncOwnedViewport(ImGuiWindow* window, ImGuiWindow* parent_win
 
     // Update parent viewport ID
     // (the !IsFallbackWindow test mimic the one done in WindowSelectViewport())
-    if (window->WindowClass.ParentViewportId)
+    if (window->WindowClass.ParentViewportId != (ImGuiID)-1)
         window->Viewport->ParentViewportId = window->WindowClass.ParentViewportId;
     else if ((window_flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_Tooltip)) && parent_window_in_stack && (!parent_window_in_stack->IsFallbackWindow || parent_window_in_stack->WasActive))
         window->Viewport->ParentViewportId = parent_window_in_stack->Viewport->ID;
diff --git a/imgui.h b/imgui.h
index 9ad5a2bc77b1..f922fc0e5542 100644
--- a/imgui.h
+++ b/imgui.h
@@ -2100,7 +2100,7 @@ struct ImGuiSizeCallbackData
 struct ImGuiWindowClass
 {
     ImGuiID             ClassId;                    // User data. 0 = Default class (unclassed). Windows of different classes cannot be docked with each others.
-    ImGuiID             ParentViewportId;           // Hint for the platform backend. If non-zero, the platform backend can create a parent<>child relationship between the platform windows. Not conforming backends are free to e.g. parent every viewport to the main viewport or not.
+    ImGuiID             ParentViewportId;           // Hint for the platform backend. -1: use default. 0: request platform backend to not parent the platform. != 0: request platform backend to create a parent<>child relationship between the platform windows. Not conforming backends are free to e.g. parent every viewport to the main viewport or not.
     ImGuiViewportFlags  ViewportFlagsOverrideSet;   // Viewport flags to set when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
     ImGuiViewportFlags  ViewportFlagsOverrideClear; // Viewport flags to clear when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
     ImGuiTabItemFlags   TabItemFlagsOverrideSet;    // [EXPERIMENTAL] TabItem flags to set when a window of this class gets submitted into a dock node tab bar. May use with ImGuiTabItemFlags_Leading or ImGuiTabItemFlags_Trailing.
@@ -2108,7 +2108,7 @@ struct ImGuiWindowClass
     bool                DockingAlwaysTabBar;        // Set to true to enforce single floating windows of this class always having their own docking node (equivalent of setting the global io.ConfigDockingAlwaysTabBar)
     bool                DockingAllowUnclassed;      // Set to true to allow windows of this class to be docked/merged with an unclassed window. // FIXME-DOCK: Move to DockNodeFlags override?
 
-    ImGuiWindowClass() { memset(this, 0, sizeof(*this)); DockingAllowUnclassed = true; }
+    ImGuiWindowClass() { memset(this, 0, sizeof(*this)); ParentViewportId = (ImGuiID)-1; DockingAllowUnclassed = true; }
 };
 
 // Data payload for Drag and Drop operations: AcceptDragDropPayload(), GetDragDropPayload()