diff --git a/include/reactos/libs/fast486/fast486.h b/include/reactos/libs/fast486/fast486.h
index c660a25c7bd..339ecb6a77e 100644
--- a/include/reactos/libs/fast486/fast486.h
+++ b/include/reactos/libs/fast486/fast486.h
@@ -378,8 +378,9 @@ typedef union _FAST486_FLAGS_REG
         ULONG Reserved2 : 1;
         ULONG Rf        : 1;
         ULONG Vm        : 1;
+        ULONG Ac        : 1;
 
-        // ULONG Reserved : 14;
+        // ULONG Reserved : 13;
     };
 } FAST486_FLAGS_REG, *PFAST486_FLAGS_REG;
 
diff --git a/lib/fast486/opcodes.c b/lib/fast486/opcodes.c
index b191e6e9c02..0c4f3d86573 100644
--- a/lib/fast486/opcodes.c
+++ b/lib/fast486/opcodes.c
@@ -4284,6 +4284,7 @@ FAST486_OPCODE_HANDLER(Fast486OpcodePopFlags)
     State->Flags.Df = NewFlags.Df;
     State->Flags.Of = NewFlags.Of;
     State->Flags.Nt = NewFlags.Nt;
+    State->Flags.Ac = NewFlags.Ac;
 
     if (Cpl == 0) State->Flags.Iopl = NewFlags.Iopl;
     if (Cpl <= State->Flags.Iopl) State->Flags.If = NewFlags.If;