diff --git a/lib/delphi/src/Thrift.Protocol.JSON.pas b/lib/delphi/src/Thrift.Protocol.JSON.pas
index f491f53..36c3d72 100644
--- a/lib/delphi/src/Thrift.Protocol.JSON.pas
+++ b/lib/delphi/src/Thrift.Protocol.JSON.pas
@@ -24,6 +24,7 @@
 interface
 
 uses
+  Character,
   Classes,
   SysUtils,
   Math,
@@ -821,9 +822,12 @@
 var buffer : TMemoryStream;
     ch  : Byte;
     wch : Word;
+    highSurogate: Char;
+    surrogatePairs: Array[0..1] of Char;
     off : Integer;
     tmp : TBytes;
 begin
+  highSurogate := #0;
   buffer := TMemoryStream.Create;
   try
     if not skipContext
@@ -862,11 +866,31 @@
            + (HexVal(tmp[1]) shl 8)
            + (HexVal(tmp[2]) shl 4)
            +  HexVal(tmp[3]);
+
       // we need to make UTF8 bytes from it, to be decoded later
-      tmp := SysUtils.TEncoding.UTF8.GetBytes(Char(wch));
-      buffer.Write( tmp[0], length(tmp));
+      if Character.IsHighSurrogate(char(wch)) then begin
+        if highSurogate <> #0
+        then raise TProtocolException.Create( TProtocolException.INVALID_DATA, 'Expected low surrogate char');
+        highSurogate := char(wch);
+      end
+      else if Character.IsLowSurrogate(char(wch)) then begin
+        if highSurogate = #0
+        then TProtocolException.Create( TProtocolException.INVALID_DATA, 'Expected high surrogate char');
+        surrogatePairs[0] := highSurogate;
+        surrogatePairs[1] := char(wch);
+        tmp := TEncoding.UTF8.GetBytes(surrogatePairs);
+        buffer.Write( tmp[0], Length(tmp));
+        highSurogate := #0;
+      end
+      else begin
+        tmp := SysUtils.TEncoding.UTF8.GetBytes(Char(wch));
+        buffer.Write( tmp[0], Length(tmp));
+      end;
     end;
 
+    if highSurogate <> #0
+    then raise TProtocolException.Create( TProtocolException.INVALID_DATA, 'Expected low surrogate char');
+
     SetLength( result, buffer.Size);
     if buffer.Size > 0 then Move( buffer.Memory^, result[0], Length(result));
 
diff --git a/lib/delphi/test/TestClient.pas b/lib/delphi/test/TestClient.pas
index 5f375ef..144334b 100644
--- a/lib/delphi/test/TestClient.pas
+++ b/lib/delphi/test/TestClient.pas
@@ -1028,9 +1028,9 @@
   TEST_DOUBLE  = -1.234e-56;
   DELTA_DOUBLE = TEST_DOUBLE * 1e-14;
   TEST_STRING  = 'abc-'#$00E4#$00f6#$00fc; // german umlauts (en-us: "funny chars")
-  // Test THRIFT-2336 with 'Русское Название';
-  RUSSIAN_TEXT = #$0420#$0443#$0441#$0441#$043a#$043e#$0435' '#$041d#$0430#$0437#$0432#$0430#$043d#$0438#$0435;
-  RUSSIAN_JSON = '"\u0420\u0443\u0441\u0441\u043a\u043e\u0435 \u041d\u0430\u0437\u0432\u0430\u043d\u0438\u0435"';
+  // Test THRIFT-2336 and THRIFT-3404 with U+1D11E (G Clef symbol) and 'Русское Название';
+  G_CLEF_AND_CYRILLIC_TEXT = #$1d11e' '#$0420#$0443#$0441#$0441#$043a#$043e#$0435' '#$041d#$0430#$0437#$0432#$0430#$043d#$0438#$0435;
+  G_CLEF_AND_CYRILLIC_JSON = '"\ud834\udd1e \u0420\u0443\u0441\u0441\u043a\u043e\u0435 \u041d\u0430\u0437\u0432\u0430\u043d\u0438\u0435"';
   // test both possible solidus encodings
   SOLIDUS_JSON_DATA = '"one/two\/three"';
   SOLIDUS_EXCPECTED = 'one/two/three';
@@ -1117,22 +1117,22 @@
     prot := TJSONProtocolImpl.Create(
               TStreamTransportImpl.Create(
                 nil, TThriftStreamAdapterDelphi.Create( stm, FALSE)));
-    prot.WriteString( RUSSIAN_TEXT);
+    prot.WriteString( G_CLEF_AND_CYRILLIC_TEXT);
     stm.Position := 0;
     prot := TJSONProtocolImpl.Create(
               TStreamTransportImpl.Create(
                 TThriftStreamAdapterDelphi.Create( stm, FALSE), nil));
-    Expect( prot.ReadString = RUSSIAN_TEXT, 'Writing JSON with chars > 8 bit');
+    Expect( prot.ReadString = G_CLEF_AND_CYRILLIC_TEXT, 'Writing JSON with chars > 8 bit');
 
     // Widechars should work with hex-encoding too. Do they?
     stm.Position := 0;
     stm.Size     := 0;
-    stm.WriteString( RUSSIAN_JSON);
+    stm.WriteString( G_CLEF_AND_CYRILLIC_JSON);
     stm.Position := 0;
     prot := TJSONProtocolImpl.Create(
               TStreamTransportImpl.Create(
                 TThriftStreamAdapterDelphi.Create( stm, FALSE), nil));
-    Expect( prot.ReadString = RUSSIAN_TEXT, 'Reading JSON with chars > 8 bit');
+    Expect( prot.ReadString = G_CLEF_AND_CYRILLIC_TEXT, 'Reading JSON with chars > 8 bit');
 
 
   finally