diff --git a/FMCTCSSRX.cpp b/FMCTCSSRX.cpp
index ade0491..57fbfbe 100644
--- a/FMCTCSSRX.cpp
+++ b/FMCTCSSRX.cpp
@@ -122,7 +122,7 @@ CTCSSState CFMCTCSSRX::process(q15_t sample)
   q31_t t3 = t2 * 2;
 
   // m_q0 = m_coeffDivTwo * m_q1 * 2 - q2 + sample
-  m_q0 = t3 - q2 + sample;
+  m_q0 = t3 - q2 + q31_t(sample);
 
   m_count++;
   if (m_count == N) {