Index: festival/src/modules/hts_engine/HTS_hidden.h
===================================================================
--- festival/src/modules/hts_engine/HTS_hidden.h
+++ festival/src/modules/hts_engine/HTS_hidden.h	2020-03-15 22:06:48.762550277 +0100
@@ -55,6 +55,11 @@
 
 HTS_HIDDEN_H_START;
 
+#ifndef INCVIS
+#define INCVIS
+#define INCVISEND
+#endif
+
 /* hts_engine libraries */
 #include "HTS_engine.h"
 
@@ -491,13 +496,19 @@
 } HTS_Vocoder;
 
 /* HTS_Vocoder_initialize: initialize vocoder */
+INCVIS
 void HTS_Vocoder_initialize(HTS_Vocoder * v, size_t m, size_t stage, HTS_Boolean use_log_gain, size_t rate, size_t fperiod);
+INCVISEND
 
 /* HTS_Vocoder_synthesize: pulse/noise excitation and MLSA/MGLSA filster based waveform synthesis */
+INCVIS
 void HTS_Vocoder_synthesize(HTS_Vocoder * v, size_t m, double lf0, double *spectrum, size_t nlpf, double *lpf, double alpha, double beta, double volume, double *rawdata, HTS_Audio * audio);
+INCVISEND
 
 /* HTS_Vocoder_clear: clear vocoder */
+INCVIS
 void HTS_Vocoder_clear(HTS_Vocoder * v);
+INCVISEND
 
 HTS_HIDDEN_H_END;
 
Index: festival/src/modules/hts_engine/HTS_vocoder.c
===================================================================
--- festival/src/modules/hts_engine/HTS_vocoder.c
+++ festival/src/modules/hts_engine/HTS_vocoder.c	2020-03-15 22:06:48.762550277 +0100
@@ -60,6 +60,11 @@
 /* hts_engine libraries */
 #include "HTS_hidden.h"
 
+#ifndef INCVIS
+#define INCVIS
+#define INCVISEND
+#endif
+
 static const double HTS_pade[21] = {
    1.00000000000,
    1.00000000000,
@@ -837,7 +842,8 @@
 }
 
 /* HTS_Vocoder_initialize: initialize vocoder */
+INCVIS
 void HTS_Vocoder_initialize(HTS_Vocoder * v, size_t m, size_t stage, HTS_Boolean use_log_gain, size_t rate, size_t fperiod)
 {
    /* set parameter */
    v->stage = stage;
@@ -878,9 +883,11 @@
    v->pulse_buff = NULL;
    v->pulse_size = 0;
 }
+INCVISEND
 
 /* HTS_Vocoder_synthesize: pulse/noise excitation and MLSA/MGLSA filster based waveform synthesis */
+INCVIS
 void HTS_Vocoder_synthesize(HTS_Vocoder * v, size_t m, double lf0, double *spectrum, size_t nlpf, double *lpf, double alpha, double beta, double volume, double *rawdata, HTS_Audio * audio)
 {
    double x;
    int i, j;
@@ -972,9 +978,11 @@
    HTS_Vocoder_end_excitation(v, nlpf);
    HTS_movem(v->cc, v->c, m + 1);
 }
+INCVISEND
 
 /* HTS_Vocoder_clear: clear vocoder */
+INCVIS
 void HTS_Vocoder_clear(HTS_Vocoder * v)
 {
    if (v != NULL) {
       /* free buffer */
@@ -1014,6 +1021,7 @@
       }
    }
 }
+INCVISEND
 
 HTS_VOCODER_C_END;
 
Index: festival/src/modules/clustergen/HTS_vocoder_me.cc
===================================================================
--- festival/src/modules/clustergen/HTS_vocoder_me.cc
+++ festival/src/modules/clustergen/HTS_vocoder_me.cc	2020-03-15 22:06:48.762550277 +0100
@@ -90,6 +90,9 @@
 
 HTS_VOCODER_ME_C_START;
 
+#define INCVIS HTS_VOCODER_ME_C_END static
+#define INCVISEND HTS_VOCODER_ME_C_START
+
 #include "./HTS_vocoder_me.h"
 #include "../hts_engine/HTS_vocoder.c"