diff --git a/Core/apu.c b/Core/apu.c
index 2b5dc3b..9275f81 100644
--- a/Core/apu.c
+++ b/Core/apu.c
@@ -230,15 +230,6 @@ static void render(GB_gameboy_t *gb)
     gb->apu_output.sample_callback(gb, &filtered_output);
 }
 
-static uint16_t new_sweep_sample_length(GB_gameboy_t *gb)
-{
-    uint16_t delta = gb->apu.shadow_sweep_sample_length >> (gb->io_registers[GB_IO_NR10] & 7);
-    if (gb->io_registers[GB_IO_NR10] & 8) {
-        return gb->apu.shadow_sweep_sample_length - delta;
-    }
-    return gb->apu.shadow_sweep_sample_length + delta;
-}
-
 static void update_square_sample(GB_gameboy_t *gb, unsigned index)
 {
     if (gb->apu.square_channels[index].current_sample_index & 0x80) return;
@@ -405,21 +396,22 @@ void GB_apu_div_event(GB_gameboy_t *gb)
     }
 
     if ((gb->apu.div_divider & 3) == 3) {
-        if (!gb->apu.sweep_enabled) {
-            return;
-        }
         if (gb->apu.square_sweep_countdown) {
-            if (!--gb->apu.square_sweep_countdown) {
+            if (!--gb->apu.square_sweep_countdown && gb->apu.sweep_enabled) {
                 if ((gb->io_registers[GB_IO_NR10] & 0x70) && (gb->io_registers[GB_IO_NR10] & 0x07)) {
                     gb->apu.square_channels[GB_SQUARE_1].sample_length =
-                        gb->apu.shadow_sweep_sample_length =
-                        gb->apu.new_sweep_sample_length;
+                    gb->apu.sweep_length_addend + gb->apu.shadow_sweep_sample_length + !!(gb->io_registers[GB_IO_NR10] & 0x8);
+                    gb->apu.square_channels[GB_SQUARE_1].sample_length &= 0x7FF;
                 }
+                gb->apu.sweep_length_addend = gb->apu.square_channels[GB_SQUARE_1].sample_length;
+                gb->apu.sweep_length_addend >>= (gb->io_registers[GB_IO_NR10] & 7);
 
                 if (gb->io_registers[GB_IO_NR10] & 0x70) {
                     /* Recalculation and overflow check only occurs after a delay */
-                    gb->apu.square_sweep_calculate_countdown = 0x13 - gb->apu.lf_div;
+                    gb->apu.square_sweep_calculate_countdown = (gb->io_registers[GB_IO_NR10] & 0x7) * 2 + 7 - gb->apu.lf_div;
                 }
+                
+                gb->apu.sweep_enabled = gb->io_registers[GB_IO_NR10] & 0x70;
 
                 gb->apu.square_sweep_countdown = ((gb->io_registers[GB_IO_NR10] >> 4) & 7);
                 if (!gb->apu.square_sweep_countdown) gb->apu.square_sweep_countdown = 8;
@@ -447,13 +439,14 @@ void GB_apu_run(GB_gameboy_t *gb)
             }
             else {
                 /* APU bug: sweep frequency is checked after adding the sweep delta twice */
-                gb->apu.new_sweep_sample_length = new_sweep_sample_length(gb);
-                if (gb->apu.new_sweep_sample_length > 0x7ff) {
+                gb->apu.shadow_sweep_sample_length = gb->apu.square_channels[GB_SQUARE_1].sample_length;
+                if (gb->io_registers[GB_IO_NR10] & 8) {
+                    gb->apu.sweep_length_addend ^= 0x7FF;
+                }
+                if (gb->apu.shadow_sweep_sample_length + gb->apu.sweep_length_addend > 0x7FF && !(gb->io_registers[GB_IO_NR10] & 8)) {
                     gb->apu.is_active[GB_SQUARE_1] = false;
                     update_sample(gb, GB_SQUARE_1, 0, gb->apu.square_sweep_calculate_countdown - cycles);
-                    gb->apu.sweep_enabled = false;
                 }
-                gb->apu.sweep_decreasing |= gb->io_registers[GB_IO_NR10] & 8;
                 gb->apu.square_sweep_calculate_countdown = 0;
             }
         }
@@ -672,10 +665,9 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
 
         /* Square channels */
         case GB_IO_NR10:
-            if (gb->apu.sweep_decreasing && !(value & 8)) {
+            if (gb->apu.shadow_sweep_sample_length + gb->apu.sweep_length_addend > 0x7FF && !(gb->io_registers[GB_IO_NR10] & 8)) {
                 gb->apu.is_active[GB_SQUARE_1] = false;
                 update_sample(gb, GB_SQUARE_1, 0, 0);
-                gb->apu.sweep_enabled = false;
                 gb->apu.square_sweep_calculate_countdown = 0;
             }
             if ((value & 0x70) == 0) {
@@ -744,12 +736,12 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
 
             gb->apu.square_channels[index].sample_length &= 0xFF;
             gb->apu.square_channels[index].sample_length |= (value & 7) << 8;
-            if (index == GB_SQUARE_1) {
-                gb->apu.shadow_sweep_sample_length =
-                    gb->apu.new_sweep_sample_length =
-                    gb->apu.square_channels[0].sample_length;
-            }
             if (value & 0x80) {
+                if (index == GB_SQUARE_1) {
+                    gb->apu.sweep_length_addend = gb->apu.square_channels[GB_SQUARE_1].sample_length;
+                    gb->apu.shadow_sweep_sample_length = 0;
+                    gb->apu.sweep_enabled = gb->io_registers[GB_IO_NR10] & 0x70;
+                }
                 /* Current sample index remains unchanged when restarting channels 1 or 2. It is only reset by
                    turning the APU off. */
                 if (!gb->apu.is_active[index]) {
@@ -782,15 +774,14 @@ void GB_apu_write(GB_gameboy_t *gb, uint8_t reg, uint8_t value)
                 }
 
                 if (index == GB_SQUARE_1) {
-                    gb->apu.sweep_decreasing = false;
                     if (gb->io_registers[GB_IO_NR10] & 7) {
                         /* APU bug: if shift is nonzero, overflow check also occurs on trigger */
-                        gb->apu.square_sweep_calculate_countdown = 0x13 - gb->apu.lf_div;
+                        gb->apu.square_sweep_calculate_countdown = (gb->io_registers[GB_IO_NR10] & 0x7) * 2 + 7 - gb->apu.lf_div;
+                        gb->apu.sweep_length_addend >>= (gb->io_registers[GB_IO_NR10] & 7);
                     }
                     else {
                         gb->apu.square_sweep_calculate_countdown = 0;
                     }
-                    gb->apu.sweep_enabled = gb->io_registers[GB_IO_NR10] & 0x77;
                     gb->apu.square_sweep_countdown = ((gb->io_registers[GB_IO_NR10] >> 4) & 7);
                     if (!gb->apu.square_sweep_countdown) gb->apu.square_sweep_countdown = 8;
                 }
diff --git a/Core/apu.h b/Core/apu.h
index a3a36a6..0512723 100644
--- a/Core/apu.h
+++ b/Core/apu.h
@@ -64,10 +64,10 @@ typedef struct
 
     uint8_t square_sweep_countdown; // In 128Hz
     uint8_t square_sweep_calculate_countdown; // In 2 MHz
-    uint16_t new_sweep_sample_length;
+    uint16_t sweep_length_addend;
     uint16_t shadow_sweep_sample_length;
     bool sweep_enabled;
-    bool sweep_decreasing;
+    GB_PADDING(bool, sweep_decreasing);
 
     struct {
         uint16_t pulse_length; // Reloaded from NRX1 (xorred), in 256Hz DIV ticks
diff --git a/Core/debugger.c b/Core/debugger.c
index 3e1b66c..28db01c 100644
--- a/Core/debugger.c
+++ b/Core/debugger.c
@@ -1780,7 +1780,7 @@ static bool apu(GB_gameboy_t *gb, char *arguments, char *modifiers, const debugg
         if (channel == GB_SQUARE_1) {
             GB_log(gb, "    Frequency sweep %s and %s (next in %u APU ticks)\n",
                    gb->apu.sweep_enabled? "active" : "inactive",
-                   gb->apu.sweep_decreasing? "decreasing" : "increasing",
+                   (gb->io_registers[GB_IO_NR10] & 0x8) ? "decreasing" : "increasing",
                    gb->apu.square_sweep_calculate_countdown);
         }