diff --git a/libraries/Filter/FilterWithBuffer.h b/libraries/Filter/FilterWithBuffer.h
index 4aa20faf06..761678fd26 100644
--- a/libraries/Filter/FilterWithBuffer.h
+++ b/libraries/Filter/FilterWithBuffer.h
@@ -40,11 +40,11 @@ public:
     void reset();
 
     // get filter size
-    uint8_t get_filter_size() {
+    uint8_t get_filter_size() const {
         return FILTER_SIZE;
     };
 
-    virtual T get_sample(uint8_t i) {
+    virtual T get_sample(uint8_t i) const {
         return samples[i];
     }