diff --git a/Marlin/Marlin.h b/Marlin/Marlin.h
index a510b4242..fac820a81 100644
--- a/Marlin/Marlin.h
+++ b/Marlin/Marlin.h
@@ -423,9 +423,9 @@ void report_current_position();
   extern bool filament_sensor;         // Flag that filament sensor readings should control extrusion
   extern float filament_width_nominal, // Theoretical filament diameter i.e., 3.00 or 1.75
                filament_width_meas;    // Measured filament diameter
-  extern uint8_t meas_delay_cm,        // Delay distance
-                 measurement_delay[];  // Ring buffer to delay measurement
-  extern int8_t filwidth_delay_index[2]; // Ring buffer indexes. Used by planner, temperature, and main code
+  extern uint8_t meas_delay_cm;        // Delay distance
+  extern int8_t measurement_delay[MAX_MEASUREMENT_DELAY + 1],  // Ring buffer to delay measurement
+                filwidth_delay_index[2]; // Ring buffer indexes. Used by planner, temperature, and main code
 #endif
 
 #if ENABLED(ADVANCED_PAUSE_FEATURE)
diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index e423474af..4e817536b 100644
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -640,9 +640,9 @@ float cartes[XYZ] = { 0 };
   bool filament_sensor = false;                                 // M405 turns on filament sensor control. M406 turns it 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
 
 #if ENABLED(FILAMENT_RUNOUT_SENSOR)
@@ -9588,7 +9588,7 @@ inline void gcode_M400() { stepper.synchronize(); }
     }
 
     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/planner.cpp b/Marlin/planner.cpp
index f69b18d2b..4e1713808 100644
--- a/Marlin/planner.cpp
+++ b/Marlin/planner.cpp
@@ -1081,7 +1081,7 @@ 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