diff --git a/imgui.cpp b/imgui.cpp
index bc1a5025b..61d5a2cfd 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -5413,10 +5413,11 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
 
         // Update various regions. Variables they depends on are set above in this function.
         // FIXME: window->ContentsRegionRect.Max is currently very misleading / partly faulty, but some BeginChild() patterns relies on it.
+        // NB: WindowBorderSize is included in WindowPadding _and_ ScrollbarSizes so we need to cancel one out.
         window->ContentsRegionRect.Min.x = window->Pos.x - window->Scroll.x + window->WindowPadding.x;
         window->ContentsRegionRect.Min.y = window->Pos.y - window->Scroll.y + window->WindowPadding.y + window->TitleBarHeight() + window->MenuBarHeight();
-        window->ContentsRegionRect.Max.x = window->Pos.x - window->Scroll.x - window->WindowPadding.x + (window->SizeContentsExplicit.x != 0.0f ? window->SizeContentsExplicit.x : (window->Size.x - window->ScrollbarSizes.x + window->WindowBorderSize));
-        window->ContentsRegionRect.Max.y = window->Pos.y - window->Scroll.y - window->WindowPadding.y + (window->SizeContentsExplicit.y != 0.0f ? window->SizeContentsExplicit.y : (window->Size.y - window->ScrollbarSizes.y + window->WindowBorderSize));
+        window->ContentsRegionRect.Max.x = window->Pos.x - window->Scroll.x - window->WindowPadding.x + (window->SizeContentsExplicit.x != 0.0f ? window->SizeContentsExplicit.x : (window->Size.x - window->ScrollbarSizes.x + ImMin(window->ScrollbarSizes.x, window->WindowBorderSize)));
+        window->ContentsRegionRect.Max.y = window->Pos.y - window->Scroll.y - window->WindowPadding.y + (window->SizeContentsExplicit.y != 0.0f ? window->SizeContentsExplicit.y : (window->Size.y - window->ScrollbarSizes.y + ImMin(window->ScrollbarSizes.y, window->WindowBorderSize)));
 
         // Save clipped aabb so we can access it in constant-time in FindHoveredWindow()
         window->OuterRectClipped = window->Rect();