diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index eac83b090..d9a95e3c1 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -78,6 +78,9 @@ Other changes:
 - ImDrawList: texture baked storage for thick line reduced from ~64x64 to ~32x32. (#3245)
 - ImFontAtlas: made calling ClearFonts() call ClearInputData(), as calling
   one without the other is never correct. (#8174, #6556, #6336, #4723)
+- ImFont: IndexLookup[] table hold 16-bit values even in ImWchar32 mode,
+  as it accounts for number of glyphs in same font. This is favorable to
+  CalcTextSize() calls touching less memory.
 - Examples: DirectX12: Reduced number of frame in flight from 3 to 2 in
   provided example, to reduce latency.
 - Examples: Vulkan: better handle VK_SUBOPTIMAL_KHR being returned by
diff --git a/imgui.h b/imgui.h
index 48910ea75..8c6082d9e 100644
--- a/imgui.h
+++ b/imgui.h
@@ -3456,7 +3456,7 @@ struct ImFont
     float                       FontSize;           // 4     // in  //            // Height of characters/line, set during loading (don't change after loading)
 
     // [Internal] Members: Hot ~28/40 bytes (for RenderText loop)
-    ImVector<ImWchar>           IndexLookup;        // 12-16 // out //            // Sparse. Index glyphs by Unicode code-point.
+    ImVector<ImU16>             IndexLookup;        // 12-16 // out //            // Sparse. Index glyphs by Unicode code-point.
     ImVector<ImFontGlyph>       Glyphs;             // 12-16 // out //            // All glyphs.
     const ImFontGlyph*          FallbackGlyph;      // 4-8   // out // = FindGlyph(FontFallbackChar)
 
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index eb5cfd51b..1a30b9a9b 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -3738,7 +3738,7 @@ void ImFont::BuildLookupTable()
     {
         int codepoint = (int)Glyphs[i].Codepoint;
         IndexAdvanceX[codepoint] = Glyphs[i].AdvanceX;
-        IndexLookup[codepoint] = (ImWchar)i;
+        IndexLookup[codepoint] = (ImU16)i;
 
         // Mark 4K page as used
         const int page_n = codepoint / 8192;
@@ -3756,7 +3756,7 @@ void ImFont::BuildLookupTable()
         tab_glyph.Codepoint = '\t';
         tab_glyph.AdvanceX *= IM_TABSIZE;
         IndexAdvanceX[(int)tab_glyph.Codepoint] = (float)tab_glyph.AdvanceX;
-        IndexLookup[(int)tab_glyph.Codepoint] = (ImWchar)(Glyphs.Size - 1);
+        IndexLookup[(int)tab_glyph.Codepoint] = (ImU16)(Glyphs.Size - 1);
     }
 
     // Mark special glyphs as not visible (note that AddGlyph already mark as non-visible glyphs with zero-size polygons)
@@ -3829,7 +3829,7 @@ void ImFont::GrowIndex(int new_size)
     if (new_size <= IndexLookup.Size)
         return;
     IndexAdvanceX.resize(new_size, -1.0f);
-    IndexLookup.resize(new_size, (ImWchar)-1);
+    IndexLookup.resize(new_size, (ImU16)-1);
 }
 
 // x0/y0/x1/y1 are offset from the character upper-left layout position, in pixels. Therefore x0/y0 are often fairly close to zero.
@@ -3872,6 +3872,7 @@ void ImFont::AddGlyph(const ImFontConfig* cfg, ImWchar codepoint, float x0, floa
     glyph.U1 = u1;
     glyph.V1 = v1;
     glyph.AdvanceX = advance_x;
+    IM_ASSERT(Glyphs.Size < 0xFFFF); // IndexLookup[] hold 16-bit values and -1 is reserved.
 
     // Compute rough surface usage metrics (+1 to account for average padding, +0.99 to round)
     // We use (U1-U0)*TexWidth instead of X1-X0 to account for oversampling.
@@ -3885,13 +3886,13 @@ void ImFont::AddRemapChar(ImWchar dst, ImWchar src, bool overwrite_dst)
     IM_ASSERT(IndexLookup.Size > 0);    // Currently this can only be called AFTER the font has been built, aka after calling ImFontAtlas::GetTexDataAs*() function.
     unsigned int index_size = (unsigned int)IndexLookup.Size;
 
-    if (dst < index_size && IndexLookup.Data[dst] == (ImWchar)-1 && !overwrite_dst) // 'dst' already exists
+    if (dst < index_size && IndexLookup.Data[dst] == (ImU16)-1 && !overwrite_dst) // 'dst' already exists
         return;
     if (src >= index_size && dst >= index_size) // both 'dst' and 'src' don't exist -> no-op
         return;
 
     GrowIndex(dst + 1);
-    IndexLookup[dst] = (src < index_size) ? IndexLookup.Data[src] : (ImWchar)-1;
+    IndexLookup[dst] = (src < index_size) ? IndexLookup.Data[src] : (ImU16)-1;
     IndexAdvanceX[dst] = (src < index_size) ? IndexAdvanceX.Data[src] : 1.0f;
 }
 
@@ -3900,8 +3901,8 @@ const ImFontGlyph* ImFont::FindGlyph(ImWchar c)
 {
     if (c >= (size_t)IndexLookup.Size)
         return FallbackGlyph;
-    const ImWchar i = IndexLookup.Data[c];
-    if (i == (ImWchar)-1)
+    const ImU16 i = IndexLookup.Data[c];
+    if (i == (ImU16)-1)
         return FallbackGlyph;
     return &Glyphs.Data[i];
 }
@@ -3910,8 +3911,8 @@ const ImFontGlyph* ImFont::FindGlyphNoFallback(ImWchar c)
 {
     if (c >= (size_t)IndexLookup.Size)
         return NULL;
-    const ImWchar i = IndexLookup.Data[c];
-    if (i == (ImWchar)-1)
+    const ImU16 i = IndexLookup.Data[c];
+    if (i == (ImU16)-1)
         return NULL;
     return &Glyphs.Data[i];
 }