diff --git a/src/cnetz/dsp.c b/src/cnetz/dsp.c
index d9c92ca..5cea636 100644
--- a/src/cnetz/dsp.c
+++ b/src/cnetz/dsp.c
@@ -855,6 +855,8 @@ void cnetz_set_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode)
 {
 	PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "DSP mode %d -> %d\n", cnetz->dsp_mode, mode);
 	cnetz->dsp_mode = mode;
+	/* we must get rid of partly received frame */
+	fsk_demod_reset(&cnetz->fsk_demod);
 }
 
 void cnetz_set_sched_dsp_mode(cnetz_t *cnetz, enum dsp_mode mode, int frames_ahead)
diff --git a/src/cnetz/fsk_fm_demod.c b/src/cnetz/fsk_fm_demod.c
index 50d5fcd..92896e3 100644
--- a/src/cnetz/fsk_fm_demod.c
+++ b/src/cnetz/fsk_fm_demod.c
@@ -501,3 +501,8 @@ void fsk_correct_sync(cnetz_t *cnetz, double offset)
 	bit_time = fmod(bit_time - offset + BITS_PER_SUPERFRAME, BITS_PER_SUPERFRAME);
 }
 
+void fsk_demod_reset(fsk_fm_demod_t *fsk)
+{
+	fsk->sync = FSK_SYNC_NONE;
+}
+
diff --git a/src/cnetz/fsk_fm_demod.h b/src/cnetz/fsk_fm_demod.h
index abc8663..50d5579 100644
--- a/src/cnetz/fsk_fm_demod.h
+++ b/src/cnetz/fsk_fm_demod.h
@@ -53,4 +53,5 @@ typedef struct fsk_fm_demod {
 int fsk_fm_init(fsk_fm_demod_t *fsk, cnetz_t *cnetz, int samplerate, double bitrate);
 void fsk_fm_demod(fsk_fm_demod_t *fsk, int16_t *samples, int length);
 void fsk_correct_sync(cnetz_t *cnetz, double offset);
+void fsk_demod_reset(fsk_fm_demod_t *fsk);