diff --git a/.gitattributes b/.gitattributes
index e8c26b5946..ec09c59620 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -13802,6 +13802,7 @@ tests/webtbs/tw25170.pp svneol=native#text/plain
 tests/webtbs/tw25198.pp svneol=native#text/plain
 tests/webtbs/tw25210.pp svneol=native#text/pascal
 tests/webtbs/tw2525.pp svneol=native#text/plain
+tests/webtbs/tw25255.pp svneol=native#text/pascal
 tests/webtbs/tw25269.pp svneol=native#text/pascal
 tests/webtbs/tw25289.pp svneol=native#text/plain
 tests/webtbs/tw25296.pp svneol=native#text/plain
diff --git a/compiler/nmat.pas b/compiler/nmat.pas
index 3e54c52f62..e9a1d37855 100644
--- a/compiler/nmat.pas
+++ b/compiler/nmat.pas
@@ -1074,15 +1074,17 @@ implementation
                pasbool8,
                pasbool16,
                pasbool32,
-               pasbool64,
+               pasbool64:
+                 v:=byte(not(boolean(int64(v))));
                bool8bit,
                bool16bit,
                bool32bit,
                bool64bit:
                  begin
-                   v:=byte(not(boolean(int64(v))));
-                   if is_cbool(left.resultdef) then
-                     v:=-v;
+                   if v=0 then
+                     v:=-1
+                   else
+                     v:=0;
                  end;
                uchar,
                uwidechar,
diff --git a/tests/webtbs/tw25255.pp b/tests/webtbs/tw25255.pp
new file mode 100644
index 0000000000..b6a00ec327
--- /dev/null
+++ b/tests/webtbs/tw25255.pp
@@ -0,0 +1,10 @@
+begin
+  if not(qwordbool($8000000000000000)) then
+    halt(1);
+  if not(longbool($80000000)) then
+    halt(1);
+  if not(wordbool($8000)) then
+    halt(1);
+  writeln('ok');
+end.
+