diff --git a/src/Graphics/Fonts/smart_font.cpp b/src/Graphics/Fonts/smart_font.cpp
index 15fd477c28..76e0d2ce69 100644
--- a/src/Graphics/Fonts/smart_font.cpp
+++ b/src/Graphics/Fonts/smart_font.cpp
@@ -1151,6 +1151,16 @@ use_italic_greek (array<string> a) {
   return count <= 1;
 }
 
+// 单个 Unicode 字符的码点；多字符串、空串或 TeXmacs 专用标记（<sqrt> 等）返回 -1
+static int
+unicode_code_of (string c) {
+  string uc= strict_cork_to_utf8 (c);
+  if (N (uc) == 0) return -1;
+  int pos = 0;
+  int code= decode_from_utf8 (uc, pos);
+  return (pos == N (uc)) ? code : -1;
+}
+
 int
 smart_font_rep::resolve (string c) {
   if (DEBUG_VERBOSE) {
@@ -1163,6 +1173,11 @@ smart_font_rep::resolve (string c) {
 
   // Special handling for emoji characters - bypass font-family restrictions
   string range= get_unicode_range (c);
+  // U+20E3 COMBINING ENCLOSING KEYCAP 与 0-9、#、* 组成键帽序列（如 U+0030 U+20E3）。
+  // lolly 把 U+2000-U+23FF 整体归为 mathsymbols，键帽因此走数学字体链；默认
+  // 数学字体没有该字形，最终渲染为 <#20E3> 占位符（#4539）。它实际是 emoji
+  // 修饰符，应与 emoji 共用回退链。
+  bool emoji_chain= (range == "emoji") || (unicode_code_of (c) == 0x20E3);
   // 如果设置了字体，就优先使用当前设置的字体
   if (fn[SUBFONT_MAIN]->supports (c)) {
     bool prefer_italic_greek= false;
@@ -1178,7 +1193,7 @@ smart_font_rep::resolve (string c) {
     }
   }
 
-  if (range == "emoji") {
+  if (emoji_chain) {
     for (int i= 0; i < N (a); i++) {
       array<string> parts= trimmed_tokenize (a[i], "=");
       if (N (parts) >= 2 && parts[0] == "emoji") {
@@ -1220,6 +1235,15 @@ smart_font_rep::resolve (string c) {
       maybe_initialize_font (nr);
       return sm->add_char (key, c);
     }
+    // 最后兜底自带的 Asana Math：其 cmap 含 U+20E3 等组合用符号
+    font asana_fn=
+        closest_font ("Asana Math", "rm", "medium", "right", sz, dpi, 1);
+    if (!is_nil (asana_fn) && asana_fn->supports (c)) {
+      tree key= tuple ("emoji-font", "Asana Math");
+      int  nr = sm->add_font (key, REWRITE_NONE);
+      maybe_initialize_font (nr);
+      return sm->add_char (key, c);
+    }
   }
 
   // Fallback Cyrillic characters to default Chinese font
diff --git a/tests/Graphics/Fonts/smart_font_test.cpp b/tests/Graphics/Fonts/smart_font_test.cpp
index cedfb1167f..e93d91c241 100644
--- a/tests/Graphics/Fonts/smart_font_test.cpp
+++ b/tests/Graphics/Fonts/smart_font_test.cpp
@@ -49,6 +49,8 @@ private slots:
   void test_noto_sans_symbols2_font_support ();
   void test_misc_symbols_fallback ();
   void test_misc_symbols_fallback_to_symbols2 ();
+  void test_keycap_combining_font_support ();
+  void test_keycap_combining_fallback ();
 };
 
 void
@@ -326,5 +328,34 @@ TestSmartFont::test_misc_symbols_fallback_to_symbols2 () {
   QVERIFY (occurs ("NotoSansSymbols2", fn_rep->fn[nr]->res_name));
 }
 
+void
+TestSmartFont::test_keycap_combining_font_support () {
+  // U+20E3 COMBINING ENCLOSING KEYCAP 必须至少被一款自带回退字体支持，
+  // 否则 emoji 回退链无处可去（4539 的前提：Asana Math cmap 含 U+20E3）
+  font asana_fn=
+      closest_font ("Asana Math", "rm", "medium", "right", 10, 600, 1);
+  font noto_fn=
+      closest_font ("Noto Sans Symbols", "rm", "medium", "right", 10, 600, 1);
+  font noto2_fn=
+      closest_font ("Noto Sans Symbols2", "rm", "medium", "right", 10, 600, 1);
+  bool supported= (!is_nil (asana_fn) && asana_fn->supports ("<#20E3>")) ||
+                  (!is_nil (noto_fn) && noto_fn->supports ("<#20E3>")) ||
+                  (!is_nil (noto2_fn) && noto2_fn->supports ("<#20E3>"));
+  QVERIFY (supported);
+}
+
+void
+TestSmartFont::test_keycap_combining_fallback () {
+  // U+20E3 落在 lolly 的 mathsymbols 区间（U+2000-U+23FF），此前走数学字体链，
+  // 默认数学字体无该字形，渲染为 <#20E3> 占位符（4539）。
+  // 现应与 emoji 共用回退链，路由到某款符号字体而非 error 字体。
+  font fn= smart_font ("sys-chinese", "rm", "medium", "right", 10, 600);
+  smart_font_rep* fn_rep= (smart_font_rep*) fn.rep;
+  int             nr    = fn_rep->resolve ("<#20E3>");
+  QVERIFY (nr >= 0);
+  QVERIFY (!occurs ("error", fn_rep->fn[nr]->res_name));
+  QVERIFY (fn_rep->fn[nr]->supports ("<#20E3>"));
+}
+
 QTEST_MAIN (TestSmartFont)
 #include "smart_font_test.moc"