diff --git a/Marlin/src/feature/filwidth.cpp b/Marlin/src/feature/filwidth.cpp
index e43a9ccd7..eca024f7d 100644
--- a/Marlin/src/feature/filwidth.cpp
+++ b/Marlin/src/feature/filwidth.cpp
@@ -29,8 +29,8 @@
 bool filament_sensor = false;                                 // M405/M406 turns filament sensor control ON/OFF.
 float filament_width_nominal = DEFAULT_NOMINAL_FILAMENT_DIA,  // Nominal filament width. Change with M404.
       filament_width_meas = DEFAULT_MEASURED_FILAMENT_DIA;    // Measured filament diameter
-uint8_t meas_delay_cm = MEASUREMENT_DELAY_CM,                 // Distance delay setting
-        measurement_delay[MAX_MEASUREMENT_DELAY + 1];         // Ring buffer to delayed measurement. Store extruder factor after subtracting 100
-int8_t filwidth_delay_index[2] = { 0, -1 };                   // Indexes into ring buffer
+uint8_t meas_delay_cm = MEASUREMENT_DELAY_CM;                 // Distance delay setting
+int8_t measurement_delay[MAX_MEASUREMENT_DELAY + 1],          // Ring buffer to delayed measurement. Store extruder factor after subtracting 100
+       filwidth_delay_index[2] = { 0, -1 };                   // Indexes into ring buffer
 
 #endif // FILAMENT_WIDTH_SENSOR
diff --git a/Marlin/src/feature/filwidth.h b/Marlin/src/feature/filwidth.h
index 436805939..1f0dfc6f0 100644
--- a/Marlin/src/feature/filwidth.h
+++ b/Marlin/src/feature/filwidth.h
@@ -25,11 +25,11 @@
 
 #include "../inc/MarlinConfig.h"
 
-extern bool filament_sensor;                                  // M405/M406 turns filament sensor control ON/OFF.
-extern float filament_width_nominal,                          // Nominal filament width. Change with M404.
-             filament_width_meas;                             // Measured filament diameter
-extern uint8_t meas_delay_cm,                                 // Distance delay setting
-               measurement_delay[MAX_MEASUREMENT_DELAY + 1];  // Ring buffer to delayed measurement. Store extruder factor after subtracting 100
-extern int8_t filwidth_delay_index[2];                        // Indexes into ring buffer
+extern bool filament_sensor;                                // M405/M406 turns filament sensor control ON/OFF.
+extern float filament_width_nominal,                        // Nominal filament width. Change with M404.
+             filament_width_meas;                           // Measured filament diameter
+extern uint8_t meas_delay_cm;                               // Distance delay setting
+extern int8_t measurement_delay[MAX_MEASUREMENT_DELAY + 1], // Ring buffer to delayed measurement. Store extruder factor after subtracting 100
+              filwidth_delay_index[2];                      // Indexes into ring buffer
 
 #endif // __FILWIDTH_H__
diff --git a/Marlin/src/gcode/feature/filwidth/M404-M407.cpp b/Marlin/src/gcode/feature/filwidth/M404-M407.cpp
index 66e47397c..a096feef1 100644
--- a/Marlin/src/gcode/feature/filwidth/M404-M407.cpp
+++ b/Marlin/src/gcode/feature/filwidth/M404-M407.cpp
@@ -56,7 +56,7 @@ void GcodeSuite::M405() {
   }
 
   if (filwidth_delay_index[1] == -1) { // Initialize the ring buffer if not done since startup
-    const uint8_t temp_ratio = thermalManager.widthFil_to_size_ratio();
+    const int8_t temp_ratio = thermalManager.widthFil_to_size_ratio();
 
     for (uint8_t i = 0; i < COUNT(measurement_delay); ++i)
       measurement_delay[i] = temp_ratio;
diff --git a/Marlin/src/module/planner.cpp b/Marlin/src/module/planner.cpp
index 1155d1d58..85c0f2010 100644
--- a/Marlin/src/module/planner.cpp
+++ b/Marlin/src/module/planner.cpp
@@ -1092,7 +1092,7 @@ void Planner::_buffer_steps(const int32_t (&target)[XYZE], float fr_mm_s, const
         // If the index has changed (must have gone forward)...
         if (filwidth_delay_index[0] != filwidth_delay_index[1]) {
           filwidth_e_count = 0; // Reset the E movement counter
-          const uint8_t meas_sample = thermalManager.widthFil_to_size_ratio();
+          const int8_t meas_sample = thermalManager.widthFil_to_size_ratio();
           do {
             filwidth_delay_index[1] = (filwidth_delay_index[1] + 1) % MMD_CM; // The next unused slot
             measurement_delay[filwidth_delay_index[1]] = meas_sample;         // Store the measurement