diff --git a/Core/gb.c b/Core/gb.c
index cc85c92..1021dd9 100644
--- a/Core/gb.c
+++ b/Core/gb.c
@@ -1854,15 +1854,6 @@ unsigned GB_time_to_alarm(GB_gameboy_t *gb)
     return alarm_time - current_time;
 }
 
-void GB_set_rtc_mode(GB_gameboy_t *gb, GB_rtc_mode_t mode)
-{
-    if (gb->rtc_mode != mode) {
-        gb->rtc_mode = mode;
-        gb->rtc_cycles = 0;
-        gb->last_rtc_second = time(NULL);
-    }
-}
-
 bool GB_has_accelerometer(GB_gameboy_t *gb)
 {
     return gb->cartridge_type->mbc_type == GB_MBC7;
diff --git a/Core/gb.h b/Core/gb.h
index d5a6471..3c77aed 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -247,11 +247,6 @@ typedef enum {
     GB_BOOT_ROM_AGB,
 } GB_boot_rom_t;
 
-typedef enum {
-    GB_RTC_MODE_SYNC_TO_HOST,
-    GB_RTC_MODE_ACCURATE,
-} GB_rtc_mode_t;
-
 #ifdef GB_INTERNAL
 #define LCDC_PERIOD 70224
 #define CPU_FREQUENCY 0x400000
@@ -640,6 +635,7 @@ struct GB_gameboy_internal_s {
         uint64_t last_sync;
         uint64_t cycles_since_last_sync; // In 8MHz units
         GB_rtc_mode_t rtc_mode;
+        uint32_t rtc_second_length;
 
         /* Audio */
         GB_apu_output_t apu_output;
@@ -861,10 +857,7 @@ void GB_disconnect_serial(GB_gameboy_t *gb);
     
 /* For cartridges with an alarm clock */
 unsigned GB_time_to_alarm(GB_gameboy_t *gb); // 0 if no alarm
-    
-/* RTC emulation mode */
-void GB_set_rtc_mode(GB_gameboy_t *gb, GB_rtc_mode_t mode);
-    
+
 /* For cartridges motion controls */
 bool GB_has_accelerometer(GB_gameboy_t *gb);
 // In units of g (gravity's acceleration).
diff --git a/Core/timing.c b/Core/timing.c
index 001869c..f8ffd80 100644
--- a/Core/timing.c
+++ b/Core/timing.c
@@ -248,11 +248,32 @@ static void advance_serial(GB_gameboy_t *gb, uint8_t cycles)
     
 }
 
+void GB_set_rtc_mode(GB_gameboy_t *gb, GB_rtc_mode_t mode)
+{
+    if (gb->rtc_mode != mode) {
+        gb->rtc_mode = mode;
+        gb->rtc_cycles = 0;
+        gb->last_rtc_second = time(NULL);
+    }
+}
+
+
+void GB_set_rtc_multiplier(GB_gameboy_t *gb, double multiplier)
+{
+    if (multiplier == 1) {
+        gb->rtc_second_length = 0;
+        return;
+    }
+    
+    gb->rtc_second_length = GB_get_unmultiplied_clock_rate(gb) * 2 * multiplier;
+}
+
 static void rtc_run(GB_gameboy_t *gb, uint8_t cycles)
 {
     if (gb->cartridge_type->mbc_type != GB_HUC3 && !gb->cartridge_type->has_rtc) return;
     gb->rtc_cycles += cycles;
     time_t current_time = 0;
+    uint32_t rtc_second_length = unlikely(gb->rtc_second_length)? gb->rtc_second_length : GB_get_unmultiplied_clock_rate(gb) * 2;
     
     switch (gb->rtc_mode) {
         case GB_RTC_MODE_SYNC_TO_HOST:
@@ -266,8 +287,8 @@ static void rtc_run(GB_gameboy_t *gb, uint8_t cycles)
                 gb->rtc_cycles -= cycles;
                 return;
             }
-            if (gb->rtc_cycles < GB_get_unmultiplied_clock_rate(gb) * 2) return;
-            gb->rtc_cycles -= GB_get_unmultiplied_clock_rate(gb) * 2;
+            if (gb->rtc_cycles < rtc_second_length) return;
+            gb->rtc_cycles -= rtc_second_length;
             current_time = gb->last_rtc_second + 1;
             break;
     }
diff --git a/Core/timing.h b/Core/timing.h
index d5d7356..96b2082 100644
--- a/Core/timing.h
+++ b/Core/timing.h
@@ -2,13 +2,23 @@
 #define timing_h
 #include "defs.h"
 
+typedef enum {
+    GB_RTC_MODE_SYNC_TO_HOST,
+    GB_RTC_MODE_ACCURATE,
+} GB_rtc_mode_t;
+
+/* RTC emulation mode */
+void GB_set_rtc_mode(GB_gameboy_t *gb, GB_rtc_mode_t mode);
+
+/* Speed multiplier for the RTC, mostly for TAS syncing */
+void GB_set_rtc_multiplier(GB_gameboy_t *gb, double multiplier);
+
 #ifdef GB_INTERNAL
 internal void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles);
 internal void GB_emulate_timer_glitch(GB_gameboy_t *gb, uint8_t old_tac, uint8_t new_tac);
 internal bool GB_timing_sync_turbo(GB_gameboy_t *gb); /* Returns true if should skip frame */
 internal void GB_timing_sync(GB_gameboy_t *gb);
 internal void GB_set_internal_div_counter(GB_gameboy_t *gb, uint16_t value);
-
 enum {
     GB_TIMA_RUNNING = 0,
     GB_TIMA_RELOADING = 1,