diff --git a/cpu/ppc/ppcemu.h b/cpu/ppc/ppcemu.h
index cce6c1b..5992da8 100644
--- a/cpu/ppc/ppcemu.h
+++ b/cpu/ppc/ppcemu.h
@@ -521,6 +521,7 @@ extern void ppc_mtfsb1();
 extern void ppc_mcrfs();
 extern void ppc_fmr();
 extern void ppc_mffs();
+extern void ppc_mffs_601();
 extern void ppc_mtfsf();
 extern void ppc_mtfsfi();
 
diff --git a/cpu/ppc/ppcexec.cpp b/cpu/ppc/ppcexec.cpp
index 9ea8c6b..0fee4c9 100644
--- a/cpu/ppc/ppcexec.cpp
+++ b/cpu/ppc/ppcexec.cpp
@@ -781,6 +781,8 @@ void ppc_cpu_init(MemCtrlBase* mem_ctrl, uint32_t cpu_version, uint64_t tb_freq)
             SubOpcode63Grabber[i + 23] = ppc_illegalop; // fsel
         }
         SubOpcode63Grabber[26]  = ppc_illegalop; // frsqrte;
+
+        SubOpcode63Grabber[583] = ppc_mffs_601;
     }
     if (cpu_version != PPC_VER::MPC970MP) {
         SubOpcode59Grabber[22] = ppc_illegalop; // fsqrts
diff --git a/cpu/ppc/ppcfpopcodes.cpp b/cpu/ppc/ppcfpopcodes.cpp
index 907e67a..f024e08 100644
--- a/cpu/ppc/ppcfpopcodes.cpp
+++ b/cpu/ppc/ppcfpopcodes.cpp
@@ -869,7 +869,16 @@ void dppc_interpreter::ppc_fmr() {
 void dppc_interpreter::ppc_mffs() {
     ppc_grab_regsda();
 
-    ppc_state.fpr[reg_d].int64_r = (uint64_t)ppc_state.fpscr;
+    ppc_state.fpr[reg_d].int64_r = (uint64_t)ppc_state.fpscr | 0xFFF8000000000000ULL;
+
+    if (rc_flag)
+        ppc_update_cr1();
+}
+
+void dppc_interpreter::ppc_mffs_601() {
+    ppc_grab_regsda();
+
+    ppc_state.fpr[reg_d].int64_r = (uint64_t)ppc_state.fpscr | 0xFFFFFFFF00000000ULL;
 
     if (rc_flag)
         ppc_update_cr1();