diff --git a/Marlin/src/HAL/AVR/fast_pwm.cpp b/Marlin/src/HAL/AVR/fast_pwm.cpp
index cdf663d5979d..e7fcbae71208 100644
--- a/Marlin/src/HAL/AVR/fast_pwm.cpp
+++ b/Marlin/src/HAL/AVR/fast_pwm.cpp
@@ -207,45 +207,46 @@ void set_pwm_frequency(const pin_t pin, const uint16_t f_desired) {
 
     // loop over prescaler values
     LOOP_L_N(i, 8) {
-      uint16_t res_temp_fast, res_temp_phase_correct;
+      uint16_t res_fast_temp, res_pc_temp;
       if (is_timer2) {
         // No resolution calculation for TIMER2 unless enabled USE_OCR2A_AS_TOP
         #if ENABLED(USE_OCR2A_AS_TOP)
-          const uint16_t rtf = (F_CPU) / (p * f_desired);
-          res_temp_fast = rtf - 1;
-          res_temp_phase_correct = rtf / 2;
+          const uint16_t rft = (F_CPU) / (p * f_desired);
+          res_fast_temp = rft - 1;
+          res_pc_temp = rft / 2;
         #else
-          res_temp_fast = res_temp_phase_correct = 255;
+          res_fast_temp = res_pc_temp = 255;
         #endif
       }
       else {
         // Skip TIMER2 specific prescalers when not TIMER2
         if (p == 32 || p == 128) continue;
-        const uint16_t rtf = (F_CPU) / (p * f_desired);
-        res_temp_fast = rtf - 1;
-        res_temp_phase_correct = rtf / 2;
+        const uint16_t rft = (F_CPU) / (p * f_desired);
+        res_fast_temp = rft - 1;
+        res_pc_temp = rft / 2;
       }
 
-      LIMIT(res_temp_fast, 1U, size);
-      LIMIT(res_temp_phase_correct, 1U, size);
+      LIMIT(res_fast_temp, 1U, size);
+      LIMIT(res_pc_temp, 1U, size);
+
       // Calculate frequencies of test prescaler and resolution values
-      const int32_t f_temp_fast = (F_CPU) / (p * (1 + res_temp_fast)),
-                    f_fast_diff = ABS(f_temp_fast - f_desired),
-                    f_diff = ABS(f - f_desired),
-                    f_temp_phase_correct = (F_CPU) / (2 * p * res_temp_phase_correct),
-                    f_phase_diff = ABS(f_temp_phase_correct - f_desired);
+      const uint32_t f_diff = _MAX(f, f_desired) - _MIN(f, f_desired),
+                     f_fast_temp = (F_CPU) / (p * (1 + res_fast_temp)),
+                     f_fast_diff = _MAX(f_fast_temp, f_desired) - _MIN(f_fast_temp, f_desired),
+                     f_pc_temp = (F_CPU) / (2 * p * res_pc_temp),
+                     f_pc_diff = _MAX(f_pc_temp, f_desired) - _MIN(f_pc_temp, f_desired);
 
-      if (f_fast_diff < f_diff && f_fast_diff <= f_phase_diff) {    // FAST values are closest to desired f
+      if (f_fast_diff < f_diff && f_fast_diff <= f_pc_diff) {    // FAST values are closest to desired f
         // Remember this combination
-        f = f_temp_fast;
-        res = res_temp_fast;
+        f = f_fast_temp;
+        res = res_fast_temp;
         j = i + 1;
         // Set the Wave Generation Mode to FAST PWM
         wgm = is_timer2 ? uint8_t(TERN(USE_OCR2A_AS_TOP, WGM2_FAST_PWM_OCR2A, WGM2_FAST_PWM)) : uint8_t(WGM_FAST_PWM_ICRn);
       }
-      else if (f_phase_diff < f_diff) {                             // PHASE CORRECT values are closes to desired f
-        f = f_temp_phase_correct;
-        res = res_temp_phase_correct;
+      else if (f_pc_diff < f_diff) {                             // PHASE CORRECT values are closes to desired f
+        f = f_pc_temp;
+        res = res_pc_temp;
         j = i + 1;
         // Set the Wave Generation Mode to PWM PHASE CORRECT
         wgm = is_timer2 ? uint8_t(TERN(USE_OCR2A_AS_TOP, WGM2_PWM_PC_OCR2A, WGM2_FAST_PWM)) : uint8_t(WGM_PWM_PC_ICRn);