diff --git a/Marlin/src/HAL/AVR/math.h b/Marlin/src/HAL/AVR/math.h
index 2bd175fde5..34f859fbbb 100644
--- a/Marlin/src/HAL/AVR/math.h
+++ b/Marlin/src/HAL/AVR/math.h
@@ -67,11 +67,9 @@ FORCE_INLINE static uint16_t MultiU24X32toH16(uint32_t longIn1, uint32_t longIn2
     A("add %[tmp2], r1")
     A("adc %A[intRes], %[tmp1]")
     A("adc %B[intRes], %[tmp1]")
-    A("lsl %[tmp2]")
-    A("adc %A[intRes], %[tmp1]")
-    A("adc %B[intRes], %[tmp1]")
     A("mul %D[longIn2], %A[longIn1]")
-    A("add %A[intRes], r0")
+    A("lsl %[tmp2]")
+    A("adc %A[intRes], r0")
     A("adc %B[intRes], r1")
     A("mul %D[longIn2], %B[longIn1]")
     A("add %B[intRes], r0")
diff --git a/Marlin/src/module/stepper.h b/Marlin/src/module/stepper.h
index 3bbfeac9ca..0706451e90 100644
--- a/Marlin/src/module/stepper.h
+++ b/Marlin/src/module/stepper.h
@@ -114,11 +114,11 @@
   #define TIMER_READ_ADD_AND_STORE_CYCLES 13UL
 
   // The base ISR
-  #define ISR_BASE_CYCLES  1000UL
+  #define ISR_BASE_CYCLES  996UL
 
   // Linear advance base time is 32 cycles
   #if ENABLED(LIN_ADVANCE)
-    #define ISR_LA_BASE_CYCLES 32UL
+    #define ISR_LA_BASE_CYCLES 30UL
   #else
     #define ISR_LA_BASE_CYCLES 0UL
   #endif