diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 143168a7..a955d1a8 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -50,6 +50,8 @@ Other Changes:
 - Scrollbar: Very minor bounding box adjustment to cope with various border size.
 - ImFontAtlas: FreeType: Added RasterizerFlags::Monochrome flag to disable font anti-aliasing. (#2545)
   Combine with RasterizerFlags::MonoHinting for best results.
+- ImFontGlyphRangesBuilder: Fixed unnecessarily over-sized buffer, which incidentally was also not
+  fully cleared. Fixed edge case overflow when adding character 0xFFFF. (#2568). [@NIKE3500]
 - Add native Mac clipboard copy/paste default implementation in core library to match what we are
   dealing with Win32, and to facilitate integration in custom engines. (#2546) [@andrewwillmott]
 - Examples/Backends: Don't filter characters under 0x10000 before calling io.AddInputCharacter(),
diff --git a/imgui.h b/imgui.h
index 75a2ae7f..77fc9c8a 100644
--- a/imgui.h
+++ b/imgui.h
@@ -1997,12 +1997,13 @@ struct ImFontGlyph
 // This is essentially a tightly packed of vector of 64k booleans = 8KB storage.
 struct ImFontGlyphRangesBuilder
 {
-    ImVector<int> UsedChars;            // Store 1-bit per Unicode code point (0=unused, 1=used)
+    ImVector<ImU32> UsedChars;            // Store 1-bit per Unicode code point (0=unused, 1=used)
 
-    ImFontGlyphRangesBuilder()          { UsedChars.resize(0x10000 / sizeof(int)); memset(UsedChars.Data, 0, 0x10000 / sizeof(int)); }
-    bool            GetBit(int n) const { int off = (n >> 5); int mask = 1 << (n & 31); return (UsedChars[off] & mask) != 0; }  // Get bit n in the array
-    void            SetBit(int n)       { int off = (n >> 5); int mask = 1 << (n & 31); UsedChars[off] |= mask; }               // Set bit n in the array
-    void            AddChar(ImWchar c)  { SetBit(c); }                          // Add character
+    ImFontGlyphRangesBuilder()          { Clear(); }
+    inline void     Clear()             { int size_in_bytes = 0x10000 / 8; UsedChars.resize(size_in_bytes / (int)sizeof(ImU32)); memset(UsedChars.Data, 0, (size_t)size_in_bytes); }
+    inline bool     GetBit(int n) const { int off = (n >> 5); ImU32 mask = 1u << (n & 31); return (UsedChars[off] & mask) != 0; }  // Get bit n in the array
+    inline void     SetBit(int n)       { int off = (n >> 5); ImU32 mask = 1u << (n & 31); UsedChars[off] |= mask; }               // Set bit n in the array
+    inline void     AddChar(ImWchar c)  { SetBit(c); }                          // Add character
     IMGUI_API void  AddText(const char* text, const char* text_end = NULL);     // Add string (each character of the UTF-8 string are added)
     IMGUI_API void  AddRanges(const ImWchar* ranges);                           // Add ranges, e.g. builder.AddRanges(ImFontAtlas::GetGlyphRangesDefault()) to force add all of ASCII/Latin+Ext
     IMGUI_API void  BuildRanges(ImVector<ImWchar>* out_ranges);                 // Output new ranges
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index bcea633b..dcbaae06 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -2391,11 +2391,12 @@ void ImFontGlyphRangesBuilder::AddRanges(const ImWchar* ranges)
 
 void ImFontGlyphRangesBuilder::BuildRanges(ImVector<ImWchar>* out_ranges)
 {
-    for (int n = 0; n < 0x10000; n++)
+    int max_codepoint = 0x10000;
+    for (int n = 0; n < max_codepoint; n++)
         if (GetBit(n))
         {
             out_ranges->push_back((ImWchar)n);
-            while (n < 0x10000 && GetBit(n + 1))
+            while (n < max_codepoint - 1 && GetBit(n + 1))
                 n++;
             out_ranges->push_back((ImWchar)n);
         }