diff --git a/Makefile.libretro b/Makefile.libretro
index e265ab3..4cc673f 100644
--- a/Makefile.libretro
+++ b/Makefile.libretro
@@ -437,9 +437,11 @@ endif
 
 LIBRETRO_CFLAGS += $(INCFLAGS) $(INCFLAGS_PLATFORM)
 LIBRETRO_CFLAGS += $(BPP_DEFINES) \
-					$(ENDIANNESS_DEFINES) \
-					$(PLATFORM_DEFINES) \
-					-D__LIBRETRO__
+		$(ENDIANNESS_DEFINES) \
+		$(PLATFORM_DEFINES) \
+		-D__LIBRETRO__ \
+		-DM68K_ALLOW_OVERCLOCK \
+		-DZ80_ALLOW_OVERCLOCK
 
 ifneq (,$(findstring msvc,$(platform)))
    LIBRETRO_CFLAGS += -DINLINE="static _inline"
diff --git a/core/m68k/m68k.h b/core/m68k/m68k.h
index 7c84334..93bb033 100644
--- a/core/m68k/m68k.h
+++ b/core/m68k/m68k.h
@@ -268,6 +268,10 @@ typedef struct
 
   uint address_space;   /* Current FC code */
 
+#ifdef M68K_ALLOW_OVERCLOCK
+  uint8 overclock_ratio;
+#endif
+
   /* Callbacks to host */
   int  (*int_ack_callback)(int int_line);           /* Interrupt Acknowledge */
   void (*reset_instr_callback)(void);               /* Called when a RESET instruction is encountered */
diff --git a/core/m68k/m68kcpu.c b/core/m68k/m68kcpu.c
index e7d762e..245bef9 100644
--- a/core/m68k/m68kcpu.c
+++ b/core/m68k/m68kcpu.c
@@ -319,6 +319,10 @@ void m68k_init(void)
   }
 #endif
 
+#ifdef M68K_ALLOW_OVERCLOCK
+  m68k.overclock_ratio = 1;
+#endif
+
 #if M68K_EMULATE_INT_ACK == OPT_ON
   m68k_set_int_ack_callback(NULL);
 #endif
diff --git a/core/m68k/m68kcpu.h b/core/m68k/m68kcpu.h
index de394b5..8b3355e 100644
--- a/core/m68k/m68kcpu.h
+++ b/core/m68k/m68kcpu.h
@@ -514,7 +514,11 @@
 
 /* ---------------------------- Cycle Counting ---------------------------- */
 
+#ifdef M68K_ALLOW_OVERCLOCK
+#define USE_CYCLES(A) m68ki_cpu.cycles += (A) / m68ki_cpu.overclock_ratio
+#else
 #define USE_CYCLES(A) m68ki_cpu.cycles += (A)
+#endif
 #define SET_CYCLES(A) m68ki_cpu.cycles  = (A)
 
 
diff --git a/core/m68k/s68kcpu.c b/core/m68k/s68kcpu.c
index 7de4652..9665085 100644
--- a/core/m68k/s68kcpu.c
+++ b/core/m68k/s68kcpu.c
@@ -284,6 +284,10 @@ void s68k_init(void)
   }
 #endif
 
+#ifdef M68K_ALLOW_OVERCLOCK
+  s68k.overclock_ratio = 1;
+#endif
+
 #if M68K_EMULATE_INT_ACK == OPT_ON
   s68k_set_int_ack_callback(NULL);
 #endif
diff --git a/core/z80/z80.c b/core/z80/z80.c
index 7a1754d..59d7f4f 100644
--- a/core/z80/z80.c
+++ b/core/z80/z80.c
@@ -201,8 +201,18 @@
 #define IFF2 Z80.iff2
 #define HALT Z80.halt
 
+#ifdef Z80_ALLOW_OVERCLOCK
+#define USE_CYCLES(A) Z80.cycles += (A) / z80_overclock_ratio
+#else
+#define USE_CYCLES(A) Z80.cycles += (A)
+#endif
+
 Z80_Regs Z80;
 
+#ifdef Z80_ALLOW_OVERCLOCK
+UINT8 z80_overclock_ratio;
+#endif
+
 unsigned char *z80_readmap[64];
 unsigned char *z80_writemap[64];
 
@@ -473,7 +483,7 @@ INLINE void BURNODD(int cycles, int opcodes, int cyclesum)
   if( cycles > 0 )
   {
     R += (cycles / cyclesum) * opcodes;
-    Z80.cycles += (cycles / cyclesum) * cyclesum * 15;
+    USE_CYCLES((cycles / cyclesum) * cyclesum * 15);
   }
 }
 
@@ -485,7 +495,7 @@ INLINE void BURNODD(int cycles, int opcodes, int cyclesum)
 /***************************************************************
  * adjust cycle count by n T-states
  ***************************************************************/
-#define CC(prefix,opcode) Z80.cycles += cc[Z80_TABLE_##prefix][opcode]
+#define CC(prefix,opcode) USE_CYCLES(cc[Z80_TABLE_##prefix][opcode])
 
 /***************************************************************
  * execute an opcode
@@ -3228,7 +3238,7 @@ static void take_interrupt(void)
     PUSH( pc );
     PCD = 0x0038;
     /* RST $38 + 'interrupt latency' cycles */
-    Z80.cycles += cc[Z80_TABLE_op][0xff] + cc[Z80_TABLE_ex][0xff];
+    USE_CYCLES(cc[Z80_TABLE_op][0xff] + cc[Z80_TABLE_ex][0xff]);
   }
   else
   {
@@ -3243,7 +3253,7 @@ static void take_interrupt(void)
       RM16( irq_vector, &Z80.pc );
       LOG(("Z80 #%d IM2 [$%04x] = $%04x\n",cpu_getactivecpu() , irq_vector, PCD));
         /* CALL $xxxx + 'interrupt latency' cycles */
-      Z80.cycles += cc[Z80_TABLE_op][0xcd] + cc[Z80_TABLE_ex][0xff];
+      USE_CYCLES(cc[Z80_TABLE_op][0xcd] + cc[Z80_TABLE_ex][0xff]);
     }
     else
     {
@@ -3257,18 +3267,18 @@ static void take_interrupt(void)
         PUSH( pc );
         PCD = irq_vector & 0xffff;
            /* CALL $xxxx + 'interrupt latency' cycles */
-        Z80.cycles += cc[Z80_TABLE_op][0xcd] + cc[Z80_TABLE_ex][0xff];
+        USE_CYCLES(cc[Z80_TABLE_op][0xcd] + cc[Z80_TABLE_ex][0xff]);
           break;
         case 0xc30000:  /* jump */
         PCD = irq_vector & 0xffff;
           /* JP $xxxx + 2 cycles */
-        Z80.cycles += cc[Z80_TABLE_op][0xc3] + cc[Z80_TABLE_ex][0xff];
+        USE_CYCLES(cc[Z80_TABLE_op][0xc3] + cc[Z80_TABLE_ex][0xff]);
           break;
         default:    /* rst (or other opcodes?) */
         PUSH( pc );
         PCD = irq_vector & 0x0038;
           /* RST $xx + 2 cycles */
-        Z80.cycles += cc[Z80_TABLE_op][0xff] + cc[Z80_TABLE_ex][0xff];
+        USE_CYCLES(cc[Z80_TABLE_op][0xff] + cc[Z80_TABLE_ex][0xff]);
           break;
       }
     }
@@ -3358,6 +3368,9 @@ void z80_init(const void *config, int (*irqcallback)(int))
   memset(&Z80, 0, sizeof(Z80));
   Z80.daisy = config;
   Z80.irq_callback = irqcallback;
+#ifdef Z80_ALLOW_OVERCLOCK
+  z80_overclock_ratio = 1;
+#endif
 
   /* Clear registers values (NB: should be random on real hardware ?) */
   AF = BC = DE = HL = SP = IX = IY =0;
@@ -3449,7 +3462,7 @@ void z80_set_nmi_line(unsigned int state)
     PCD = 0x0066;
     WZ=PCD;
 
-    Z80.cycles += 11*15;
+    USE_CYCLES(11*15);
   }
 
   Z80.nmi_state = state;
diff --git a/core/z80/z80.h b/core/z80/z80.h
index d505775..8ee5f6b 100644
--- a/core/z80/z80.h
+++ b/core/z80/z80.h
@@ -51,6 +51,10 @@ typedef struct
 
 extern Z80_Regs Z80;
 
+#ifdef Z80_ALLOW_OVERCLOCK
+extern UINT8 z80_overclock_ratio;
+#endif
+
 extern unsigned char *z80_readmap[64];
 extern unsigned char *z80_writemap[64];
 
diff --git a/libretro/libretro.c b/libretro/libretro.c
index b6e3ccf..0921d4d 100644
--- a/libretro/libretro.c
+++ b/libretro/libretro.c
@@ -54,6 +54,12 @@
 #include <xtl.h>
 #endif
 
+#if defined(M68K_ALLOW_OVERCLOCK) || defined(Z80_ALLOW_OVERCLOCK)
+#define HAVE_OVERCLOCK
+/* Overclocking frame delay (hack) */
+#define OVERCLOCK_FRAME_DELAY 100
+#endif
+
 #define RETRO_DEVICE_MDPAD_3B             RETRO_DEVICE_SUBCLASS(RETRO_DEVICE_JOYPAD, 0)
 #define RETRO_DEVICE_MDPAD_6B             RETRO_DEVICE_SUBCLASS(RETRO_DEVICE_JOYPAD, 1)
 #define RETRO_DEVICE_MSPAD_2B             RETRO_DEVICE_SUBCLASS(RETRO_DEVICE_JOYPAD, 2)
@@ -150,6 +156,14 @@ static char ggvalidchars[] = "ABCDEFGHJKLMNPRSTVWXYZ0123456789";
 
 static char arvalidchars[] = "0123456789ABCDEF";
 
+/* Some games appear to calibrate music playback speed for PAL/NTSC by
+   actually counting CPU cycles per frame during startup, resulting in
+   hilariously fast music.  Delay overclocking for a while as a
+   workaround */
+#ifdef HAVE_OVERCLOCK
+static uint32_t overclock_delay;
+#endif
+
 #define SOUND_FREQUENCY 44100
 
 /* Hide the EQ settings for now */
@@ -526,6 +540,9 @@ static void config_default(void)
    config.bios           = 0;
    config.lock_on        = 0;
    config.lcd            = 0; /* 0.8 fixed point */
+#ifdef HAVE_OVERCLOCK
+   config.overclock      = 0;
+#endif
 
    /* video options */
    config.overscan = 0;
@@ -1236,8 +1253,22 @@ static void check_variables(void)
       config.invert_mouse = 1;
   }
 
+#ifdef HAVE_OVERCLOCK
+  var.key = "genesis_plus_gx_overclock";
+  environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var);
+  {
+    if (strcmp(var.value, "1x") == 0)
+      config.overclock = 0;
+    else if (strcmp(var.value, "2x") == 0)
+      config.overclock = 1;
+  }
+#endif
+
   if (reinit)
   {
+#ifdef HAVE_OVERCLOCK
+    overclock_delay = OVERCLOCK_FRAME_DELAY;
+#endif
     audio_init(SOUND_FREQUENCY, 0);
     memcpy(temp, sram.sram, sizeof(temp));
     system_init();
@@ -1677,6 +1708,9 @@ void retro_set_environment(retro_environment_t cb)
       { "genesis_plus_gx_render", "Interlaced mode 2 output; single field|double field" },
       { "genesis_plus_gx_gun_cursor", "Show Lightgun crosshair; disabled|enabled" },
       { "genesis_plus_gx_invert_mouse", "Invert Mouse Y-axis; disabled|enabled" },
+#ifdef HAVE_OVERCLOCK
+      { "genesis_plus_gx_overclock", "Overclock CPU; 1x|2x" },
+#endif
       { NULL, NULL },
    };
 
@@ -2020,6 +2054,10 @@ bool retro_unserialize(const void *data, size_t size)
    if (!state_load((uint8_t*)data))
       return FALSE;
 
+#ifdef HAVE_OVERCLOCK
+   overclock_delay = OVERCLOCK_FRAME_DELAY;
+#endif
+
    return TRUE;
 }
 
@@ -2184,6 +2222,9 @@ bool retro_load_game(const struct retro_game_info *info)
       }
    }
 
+#ifdef HAVE_OVERCLOCK
+   overclock_delay = OVERCLOCK_FRAME_DELAY;
+#endif
    audio_init(SOUND_FREQUENCY, 0);
    system_init();
    system_reset();
@@ -2299,6 +2340,9 @@ void retro_deinit(void)
 
 void retro_reset(void)
 {
+#ifdef HAVE_OVERCLOCK
+   overclock_delay = OVERCLOCK_FRAME_DELAY;
+#endif
    gen_reset(0);
 }
 
@@ -2307,12 +2351,42 @@ void retro_run(void)
    bool updated = false;
    is_running = true;
 
+#ifdef HAVE_OVERCLOCK
+  /* update overclock delay */
+  if (overclock_delay)
+      overclock_delay--;
+#endif
+
    if (system_hw == SYSTEM_MCD)
+   {
+#ifdef M68K_ALLOW_OVERCLOCK
+      if (config.overclock && overclock_delay == 0)
+         m68k.overclock_ratio = 2;
+      else
+         m68k.overclock_ratio = 1;
+#endif
       system_frame_scd(0);
+   }
    else if ((system_hw & SYSTEM_PBC) == SYSTEM_MD)
+   {
+#ifdef M68K_ALLOW_OVERCLOCK
+      if (config.overclock && overclock_delay == 0)
+         m68k.overclock_ratio = 2;
+      else
+         m68k.overclock_ratio = 1;
+#endif
       system_frame_gen(0);
+   }
    else
+   {
+#ifdef Z80_ALLOW_OVERCLOCK
+      if (config.overclock && overclock_delay == 0)
+         z80_overclock_ratio = 2;
+      else
+         z80_overclock_ratio = 1;
+#endif
       system_frame_sms(0);
+   }
 
    if (bitmap.viewport.changed & 9)
    {
diff --git a/libretro/osd.h b/libretro/osd.h
index aaa8890..089bb90 100644
--- a/libretro/osd.h
+++ b/libretro/osd.h
@@ -120,6 +120,7 @@ struct
   t_input_config input[MAX_INPUTS];
   uint8 invert_mouse;
   uint8 gun_cursor;
+  uint8 overclock;
 } config;
 
 extern char GG_ROM[256];