diff --git a/imgui.cpp b/imgui.cpp
index 06476e2cf..01f8052f3 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -5742,7 +5742,10 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             // Window background
             ImU32 bg_col = GetColorU32(GetWindowBgColorIdxFromFlags(flags));
             if (g.NextWindowData.BgAlphaCond != 0)
+            {
                 bg_col = (bg_col & ~IM_COL32_A_MASK) | (IM_F32_TO_INT8_SAT(g.NextWindowData.BgAlphaVal) << IM_COL32_A_SHIFT);
+                g.NextWindowData.BgAlphaCond = 0;
+            }
             window->DrawList->AddRectFilled(window->Pos+ImVec2(0,window->TitleBarHeight()), window->Pos+window->Size, bg_col, window_rounding, (flags & ImGuiWindowFlags_NoTitleBar) ? ImDrawCornerFlags_All : ImDrawCornerFlags_Bot);
 
             // Title bar
@@ -5965,19 +5968,19 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     return !window->SkipItems;
 }
 
-// Old Begin() API with 5 parameters, avoid calling this version directly! Use SetNextWindowSize()+Begin() instead.
+// Old Begin() API with 5 parameters, avoid calling this version directly! Use SetNextWindowSize()/SetNextWindowBgAlpha() + Begin() instead.
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
-bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_use, float bg_alpha_override, ImGuiWindowFlags flags)
+bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_first_use, float bg_alpha_override, ImGuiWindowFlags flags)
 {
-    // Old API feature: we could pass the initial window size as a parameter, however this was very misleading because in most cases it would only affect the window when it didn't have storage in the .ini file.
-    if (size_on_first_use.x != 0.0f || size_on_first_use.y != 0.0f)
-        ImGui::SetNextWindowSize(size_on_first_use, ImGuiCond_FirstUseEver);
+    // Old API feature: we could pass the initial window size as a parameter. This was misleading because it only had an effect if the window didn't have data in the .ini file.
+    if (size_first_use.x != 0.0f || size_first_use.y != 0.0f)
+        ImGui::SetNextWindowSize(size_first_use, ImGuiCond_FirstUseEver);
 
     // Old API feature: override the window background alpha with a parameter.
-    ImGui::SetNextWindowBgAlpha(bg_alpha_override);
+    if (bg_alpha_override >= 0.0f)
+        ImGui::SetNextWindowBgAlpha(bg_alpha_override);
 
-    bool ret = ImGui::Begin(name, p_open, flags);
-    return ret;
+    return ImGui::Begin(name, p_open, flags);
 }
 #endif // IMGUI_DISABLE_OBSOLETE_FUNCTIONS
 
diff --git a/imgui.h b/imgui.h
index f98bc8106..f9a4e0029 100644
--- a/imgui.h
+++ b/imgui.h
@@ -1049,7 +1049,7 @@ namespace ImGui
     static inline void  SetNextWindowContentWidth(float w)    { SetNextWindowContentSize(ImVec2(w, 0.0f)); }
     static inline float GetItemsLineHeightWithSpacing()       { return GetFrameHeightWithSpacing(); }
     // OBSOLETED in 1.52 (between Aug 2017 and Oct 2017)
-    bool                Begin(const char* name, bool* p_open, const ImVec2& size_on_first_use, float bg_alpha_override = -1.0f, ImGuiWindowFlags flags = 0); // Use SetNextWindowSize() instead if you want to set a window size.
+    bool                Begin(const char* name, bool* p_open, const ImVec2& size_on_first_use, float bg_alpha_override = -1.0f, ImGuiWindowFlags flags = 0); // Use SetNextWindowSize(size, ImGuiCond_FirstUseEver) + SetNextWindowBgAlpha() instead.
     static inline bool  IsRootWindowOrAnyChildHovered()       { return IsItemHovered(ImGuiHoveredFlags_RootAndChildWindows); }
     static inline void  AlignFirstTextHeightToWidgets()       { AlignTextToFramePadding(); }
     static inline void  SetNextWindowPosCenter(ImGuiCond c=0) { ImGuiIO& io = GetIO(); SetNextWindowPos(ImVec2(io.DisplaySize.x * 0.5f, io.DisplaySize.y * 0.5f), c, ImVec2(0.5f, 0.5f)); }