diff --git a/.gitattributes b/.gitattributes
index 61ef951615..4a41189945 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -18605,6 +18605,7 @@ tests/webtbs/tw3814.pp svneol=native#text/plain
 tests/webtbs/tw38145a.pp svneol=native#text/pascal
 tests/webtbs/tw38145b.pp svneol=native#text/pascal
 tests/webtbs/tw38151.pp svneol=native#text/pascal
+tests/webtbs/tw38202.pp svneol=native#text/pascal
 tests/webtbs/tw3827.pp svneol=native#text/plain
 tests/webtbs/tw3829.pp svneol=native#text/plain
 tests/webtbs/tw3833.pp svneol=native#text/plain
diff --git a/rtl/inc/genmath.inc b/rtl/inc/genmath.inc
index 4acaa3337d..c1574b224b 100644
--- a/rtl/inc/genmath.inc
+++ b/rtl/inc/genmath.inc
@@ -2087,7 +2087,7 @@ function TDoubleRec.GetFrac : QWord;
 
 procedure TDoubleRec.SetFrac(e : QWord);
   begin
-    Data:=(Data and $7ff0000000000000) or (e and $fffffffffffff);
+    Data:=(Data and $fff0000000000000) or (e and $fffffffffffff);
   end;
 
 {
diff --git a/tests/webtbs/tw38202.pp b/tests/webtbs/tw38202.pp
new file mode 100644
index 0000000000..de0830de5b
--- /dev/null
+++ b/tests/webtbs/tw38202.pp
@@ -0,0 +1,21 @@
+program Project1;
+
+{$mode objfpc}{$H+}
+
+uses
+  SysUtils;
+
+var
+  D: Double;
+  Q: QWord;
+
+begin
+  D := -1;
+
+  Q := D.Frac;
+  D.Frac := Q; // the sign is lost!
+
+  if D<>-1 then
+    halt(1);
+  WriteLn('ok');
+end.