diff --git a/ide/project.pp b/ide/project.pp
index b5a042216a..9cb3c95764 100644
--- a/ide/project.pp
+++ b/ide/project.pp
@@ -7000,6 +7000,7 @@ end;
 procedure TProjectBuildMode.Assign(Src: TProjectBuildMode);
 begin
   if Equals(Src) then exit;
+  InSession:=Src.InSession;
   CompilerOptions.Assign(Src.CompilerOptions);
   MacroValues.Assign(Src.MacroValues);
 end;