diff --git a/src/rvoice/fluid_chorus.c b/src/rvoice/fluid_chorus.c
index 83a88d38..abcd4bc0 100644
--- a/src/rvoice/fluid_chorus.c
+++ b/src/rvoice/fluid_chorus.c
@@ -383,7 +383,7 @@ fluid_chorus_set(fluid_chorus_t *chorus, int set, int nr, fluid_real_t level,
 }
 
 
-void fluid_chorus_processmix(fluid_chorus_t *chorus, fluid_real_t *in,
+void fluid_chorus_processmix(fluid_chorus_t *chorus, const fluid_real_t *in,
                              fluid_real_t *left_out, fluid_real_t *right_out)
 {
     int sample_index;
@@ -456,7 +456,7 @@ void fluid_chorus_processmix(fluid_chorus_t *chorus, fluid_real_t *in,
 }
 
 /* Duplication of code ... (replaces sample data instead of mixing) */
-void fluid_chorus_processreplace(fluid_chorus_t *chorus, fluid_real_t *in,
+void fluid_chorus_processreplace(fluid_chorus_t *chorus, const fluid_real_t *in,
                                  fluid_real_t *left_out, fluid_real_t *right_out)
 {
     int sample_index;
diff --git a/src/rvoice/fluid_chorus.h b/src/rvoice/fluid_chorus.h
index 8a6734aa..94130957 100644
--- a/src/rvoice/fluid_chorus.h
+++ b/src/rvoice/fluid_chorus.h
@@ -55,9 +55,9 @@ void fluid_chorus_reset(fluid_chorus_t *chorus);
 void fluid_chorus_set(fluid_chorus_t *chorus, int set, int nr, fluid_real_t level,
                       fluid_real_t speed, fluid_real_t depth_ms, int type);
 
-void fluid_chorus_processmix(fluid_chorus_t *chorus, fluid_real_t *in,
+void fluid_chorus_processmix(fluid_chorus_t *chorus, const fluid_real_t *in,
                              fluid_real_t *left_out, fluid_real_t *right_out);
-void fluid_chorus_processreplace(fluid_chorus_t *chorus, fluid_real_t *in,
+void fluid_chorus_processreplace(fluid_chorus_t *chorus, const fluid_real_t *in,
                                  fluid_real_t *left_out, fluid_real_t *right_out);
 
 
diff --git a/src/rvoice/fluid_rev.c b/src/rvoice/fluid_rev.c
index 8a58d1e8..c025e105 100644
--- a/src/rvoice/fluid_rev.c
+++ b/src/rvoice/fluid_rev.c
@@ -368,7 +368,7 @@ fluid_revmodel_reset(fluid_revmodel_t *rev)
 }
 
 void
-fluid_revmodel_processreplace(fluid_revmodel_t *rev, fluid_real_t *in,
+fluid_revmodel_processreplace(fluid_revmodel_t *rev, const fluid_real_t *in,
                               fluid_real_t *left_out, fluid_real_t *right_out)
 {
     int i, k = 0;
@@ -410,7 +410,7 @@ fluid_revmodel_processreplace(fluid_revmodel_t *rev, fluid_real_t *in,
 }
 
 void
-fluid_revmodel_processmix(fluid_revmodel_t *rev, fluid_real_t *in,
+fluid_revmodel_processmix(fluid_revmodel_t *rev, const fluid_real_t *in,
                           fluid_real_t *left_out, fluid_real_t *right_out)
 {
     int i, k = 0;
diff --git a/src/rvoice/fluid_rev.h b/src/rvoice/fluid_rev.h
index 69c00ea7..75ab5d23 100644
--- a/src/rvoice/fluid_rev.h
+++ b/src/rvoice/fluid_rev.h
@@ -61,10 +61,10 @@ typedef struct _fluid_revmodel_presets_t
 fluid_revmodel_t *new_fluid_revmodel(fluid_real_t sample_rate);
 void delete_fluid_revmodel(fluid_revmodel_t *rev);
 
-void fluid_revmodel_processmix(fluid_revmodel_t *rev, fluid_real_t *in,
+void fluid_revmodel_processmix(fluid_revmodel_t *rev, const fluid_real_t *in,
                                fluid_real_t *left_out, fluid_real_t *right_out);
 
-void fluid_revmodel_processreplace(fluid_revmodel_t *rev, fluid_real_t *in,
+void fluid_revmodel_processreplace(fluid_revmodel_t *rev, const fluid_real_t *in,
                                    fluid_real_t *left_out, fluid_real_t *right_out);
 
 void fluid_revmodel_reset(fluid_revmodel_t *rev);
diff --git a/src/rvoice/fluid_rvoice_mixer.c b/src/rvoice/fluid_rvoice_mixer.c
index 3b264e4d..fc717306 100644
--- a/src/rvoice/fluid_rvoice_mixer.c
+++ b/src/rvoice/fluid_rvoice_mixer.c
@@ -130,8 +130,8 @@ fluid_rvoice_mixer_process_fx(fluid_rvoice_mixer_t *mixer, int current_blockcoun
     const int fx_channels_per_unit = mixer->buffers.fx_buf_count / mixer->fx_units;
     int i, f;
 
-    void (*reverb_process_func)(fluid_revmodel_t *rev, fluid_real_t *in, fluid_real_t *left_out, fluid_real_t *right_out);
-    void (*chorus_process_func)(fluid_chorus_t *chorus, fluid_real_t *in, fluid_real_t *left_out, fluid_real_t *right_out);
+    void (*reverb_process_func)(fluid_revmodel_t *rev, const fluid_real_t *in, fluid_real_t *left_out, fluid_real_t *right_out);
+    void (*chorus_process_func)(fluid_chorus_t *chorus, const fluid_real_t *in, fluid_real_t *left_out, fluid_real_t *right_out);
 
     fluid_real_t *out_rev_l, *out_rev_r, *out_ch_l, *out_ch_r;
 
@@ -375,7 +375,7 @@ get_dest_buf(fluid_rvoice_buffers_t *buffers, int index,
  */
 static void
 fluid_rvoice_buffers_mix(fluid_rvoice_buffers_t *buffers,
-                         fluid_real_t *FLUID_RESTRICT dsp_buf,
+                         const fluid_real_t *FLUID_RESTRICT dsp_buf,
                          int start_block, int sample_count,
                          fluid_real_t **dest_bufs, int dest_bufcount)
 {
diff --git a/src/synth/fluid_synth.c b/src/synth/fluid_synth.c
index 0a76257d..2e29428f 100644
--- a/src/synth/fluid_synth.c
+++ b/src/synth/fluid_synth.c
@@ -3939,7 +3939,7 @@ fluid_synth_write_s16(fluid_synth_t *synth, int len,
  * @note Currently private to libfluidsynth.
  */
 void
-fluid_synth_dither_s16(int *dither_index, int len, float *lin, float *rin,
+fluid_synth_dither_s16(int *dither_index, int len, const float *lin, const float *rin,
                        void *lout, int loff, int lincr,
                        void *rout, int roff, int rincr)
 {
diff --git a/src/synth/fluid_synth.h b/src/synth/fluid_synth.h
index 95e2c2e5..156424af 100644
--- a/src/synth/fluid_synth.h
+++ b/src/synth/fluid_synth.h
@@ -190,7 +190,7 @@ fluid_preset_t *fluid_synth_find_preset(fluid_synth_t *synth,
                                         int prognum);
 void fluid_synth_sfont_unref(fluid_synth_t *synth, fluid_sfont_t *sfont);
 
-void fluid_synth_dither_s16(int *dither_index, int len, float *lin, float *rin,
+void fluid_synth_dither_s16(int *dither_index, int len, const float *lin, const float *rin,
                             void *lout, int loff, int lincr,
                             void *rout, int roff, int rincr);