diff --git a/firmware/baseband/dsp_demodulate.hpp b/firmware/baseband/dsp_demodulate.hpp
index c5f871e1..51c9504d 100644
--- a/firmware/baseband/dsp_demodulate.hpp
+++ b/firmware/baseband/dsp_demodulate.hpp
@@ -37,6 +37,12 @@ public:
 
 class FM {
 public:
+	constexpr FM(
+	) : z_ { 0 },
+		k { 0 }
+	{
+	}
+	
 	/*
 	 * angle: -pi to pi. output range: -32768 to 32767.
 	 * Maximum delta-theta (output of atan2) at maximum deviation frequency: