diff --git a/effect_modulated_delay.cpp b/effect_modulated_delay.cpp
index f3ad4df..3358d32 100644
--- a/effect_modulated_delay.cpp
+++ b/effect_modulated_delay.cpp
@@ -64,8 +64,8 @@ boolean AudioEffectModulatedDelay::begin(short *delayline, int d_length)
   modulator_filter_coeffs[0] = 0.291938819295525787;  // b0
   modulator_filter_coeffs[1] = 0.582700575839973478;  // b1
   modulator_filter_coeffs[2] = 0.291938819295525787;  // b2
-  modulator_filter_coeffs[3] = -0.005242268129729576; // a1
-  modulator_filter_coeffs[4] = 0.171820482560754689;  // a2
+  modulator_filter_coeffs[3] = 0.005242268129729576;  // -a1
+  modulator_filter_coeffs[4] = -0.171820482560754689;  // -a2
   modulator_filter_data = {1, &modulator_filter_state, modulator_filter_coeffs};
 
   return (true);