diff --git a/reactos/lib/fast486/common.c b/reactos/lib/fast486/common.c
index c776d2f53b3..9cbc8217f6c 100644
--- a/reactos/lib/fast486/common.c
+++ b/reactos/lib/fast486/common.c
@@ -699,7 +699,7 @@ Fast486TaskSwitch(PFAST486_STATE State, FAST486_TASK_SWITCH_TYPE Type, USHORT Se
             return FALSE;
         }
 
-        if (Fast486ReadDescriptorEntry(State,
+        if (!Fast486ReadDescriptorEntry(State,
                                        NewTss.Ldtr,
                                        &Valid,
                                        (PFAST486_GDT_ENTRY)&GdtEntry))
diff --git a/reactos/lib/fast486/opgroups.c b/reactos/lib/fast486/opgroups.c
index 2c99e470c08..5f1f9c73578 100644
--- a/reactos/lib/fast486/opgroups.c
+++ b/reactos/lib/fast486/opgroups.c
@@ -1847,7 +1847,7 @@ FAST486_OPCODE_HANDLER(Fast486ExtOpcodeGroup0F00)
                 return;
             }
 
-            if (Fast486ReadDescriptorEntry(State,
+            if (!Fast486ReadDescriptorEntry(State,
                                            Selector,
                                            &Valid,
                                            (PFAST486_GDT_ENTRY)&GdtEntry))