diff --git a/src/bindings/fluid_cmd.c b/src/bindings/fluid_cmd.c
index c91dde6c..aebe9e6c 100644
--- a/src/bindings/fluid_cmd.c
+++ b/src/bindings/fluid_cmd.c
@@ -75,7 +75,7 @@ typedef struct {
   const char *help;             /**< A help string */
 } fluid_cmd_int_t;
 
-static int fluid_shell_run(fluid_shell_t* shell);
+static fluid_thread_return_t fluid_shell_run(void* data);
 static void fluid_shell_init(fluid_shell_t* shell,
                              fluid_settings_t* settings, fluid_cmd_handler_t* handler,
                              fluid_istream_t in, fluid_ostream_t out);
@@ -270,7 +270,7 @@ new_fluid_shell(fluid_settings_t* settings, fluid_cmd_handler_t* handler,
   fluid_shell_init(shell, settings, handler, in, out);
 
   if (thread) {
-    shell->thread = new_fluid_thread("shell", (fluid_thread_func_t) fluid_shell_run, shell,
+    shell->thread = new_fluid_thread("shell", fluid_shell_run, shell,
                                      0, TRUE);
     if (shell->thread == NULL) {
       delete_fluid_shell(shell);
@@ -309,13 +309,14 @@ delete_fluid_shell(fluid_shell_t* shell)
   FLUID_FREE(shell);
 }
 
-static int
-fluid_shell_run(fluid_shell_t* shell)
+static fluid_thread_return_t
+fluid_shell_run(void* data)
 {
+  fluid_shell_t* shell = (fluid_shell_t*)data;
   char workline[FLUID_WORKLINELENGTH];
   char* prompt = NULL;
   int cont = 1;
-  int errors = 0;
+  int errors = FALSE;
   int n;
 
   if (shell->settings)
@@ -343,7 +344,7 @@ fluid_shell_run(fluid_shell_t* shell)
       break;
 
     case -1: /* erronous command */
-      errors++;
+      errors |= TRUE;
     case 0: /* valid command */
       break;
 
@@ -359,7 +360,7 @@ fluid_shell_run(fluid_shell_t* shell)
 
   if (prompt) FLUID_FREE (prompt);      /* -- free prompt */
 
-  return errors;
+  return errors ? (fluid_thread_return_t)(-1) : FLUID_THREAD_RETURN_VALUE;
 }
 
 /**
@@ -380,7 +381,7 @@ fluid_usershell(fluid_settings_t* settings, fluid_cmd_handler_t* handler)
  * Execute shell commands in a file.
  * @param handler Command handler callback
  * @param filename File name
- * @return 0 on success, a value >1 on error
+ * @return 0 on success, a negative value on error
  */
 int
 fluid_source(fluid_cmd_handler_t* handler, const char *filename)
@@ -398,7 +399,7 @@ fluid_source(fluid_cmd_handler_t* handler, const char *filename)
     return file;
   }
   fluid_shell_init(&shell, NULL, handler, file, fluid_get_stdout());
-  result = fluid_shell_run(&shell);
+  result = (fluid_shell_run(&shell) == FLUID_THREAD_RETURN_VALUE) ? 0 : -1;
 
 #ifdef WIN32
   _close(file);
@@ -2472,9 +2473,11 @@ struct _fluid_client_t {
 };
 
 
-static void fluid_client_run(fluid_client_t* client)
+static fluid_thread_return_t fluid_client_run(void* data)
 {
   fluid_shell_t shell;
+  fluid_client_t* client = (fluid_client_t*)data;
+  
   fluid_shell_init(&shell,
 		  client->settings,
 		  client->handler,
@@ -2483,6 +2486,8 @@ static void fluid_client_run(fluid_client_t* client)
   fluid_shell_run(&shell);
   fluid_server_remove_client(client->server, client);
   delete_fluid_client(client);
+  
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 
@@ -2501,7 +2506,7 @@ new_fluid_client(fluid_server_t* server, fluid_settings_t* settings, fluid_socke
   client->socket = sock;
   client->settings = settings;
   client->handler = new_fluid_cmd_handler(server->synth, server->router);
-  client->thread = new_fluid_thread("client", (fluid_thread_func_t) fluid_client_run, client,
+  client->thread = new_fluid_thread("client", fluid_client_run, client,
                                     0, FALSE);
 
   if (client->handler == NULL || client->thread == NULL) {
diff --git a/src/drivers/fluid_alsa.c b/src/drivers/fluid_alsa.c
index dce95158..c9482f8c 100644
--- a/src/drivers/fluid_alsa.c
+++ b/src/drivers/fluid_alsa.c
@@ -72,8 +72,8 @@ fluid_audio_driver_t* new_fluid_alsa_audio_driver2(fluid_settings_t* settings,
 
 int delete_fluid_alsa_audio_driver(fluid_audio_driver_t* p);
 void fluid_alsa_audio_driver_settings(fluid_settings_t* settings);
-static void fluid_alsa_audio_run_float(void* d);
-static void fluid_alsa_audio_run_s16(void* d);
+static fluid_thread_return_t fluid_alsa_audio_run_float(void* d);
+static fluid_thread_return_t fluid_alsa_audio_run_s16(void* d);
 
 
 struct fluid_alsa_formats_t {
@@ -118,7 +118,7 @@ fluid_midi_driver_t* new_fluid_alsa_rawmidi_driver(fluid_settings_t* settings,
 						   void* event_handler_data);
 
 int delete_fluid_alsa_rawmidi_driver(fluid_midi_driver_t* p);
-static void fluid_alsa_midi_run(void* d);
+static fluid_thread_return_t fluid_alsa_midi_run(void* d);
 
 
 /*
@@ -139,7 +139,7 @@ fluid_midi_driver_t* new_fluid_alsa_seq_driver(fluid_settings_t* settings,
 					     handle_midi_event_func_t handler,
 					     void* data);
 int delete_fluid_alsa_seq_driver(fluid_midi_driver_t* p);
-static void fluid_alsa_seq_run(void* d);
+static fluid_thread_return_t fluid_alsa_seq_run(void* d);
 
 /**************************************************************
  *
@@ -377,7 +377,7 @@ static int fluid_alsa_handle_write_error (snd_pcm_t *pcm, int errval)
   return FLUID_OK;
 }
 
-static void fluid_alsa_audio_run_float (void *d)
+static fluid_thread_return_t fluid_alsa_audio_run_float (void *d)
 {
   fluid_alsa_audio_driver_t* dev = (fluid_alsa_audio_driver_t*) d;
   fluid_synth_t *synth = (fluid_synth_t *)(dev->data);
@@ -450,9 +450,11 @@ static void fluid_alsa_audio_run_float (void *d)
 
   FLUID_FREE(left);
   FLUID_FREE(right);
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
-static void fluid_alsa_audio_run_s16 (void *d)
+static fluid_thread_return_t fluid_alsa_audio_run_s16 (void *d)
 {
   fluid_alsa_audio_driver_t* dev = (fluid_alsa_audio_driver_t*) d;
   float* left;
@@ -535,6 +537,8 @@ static void fluid_alsa_audio_run_s16 (void *d)
   FLUID_FREE(left);
   FLUID_FREE(right);
   FLUID_FREE(buf);
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 
@@ -674,7 +678,7 @@ delete_fluid_alsa_rawmidi_driver(fluid_midi_driver_t* p)
 /*
  * fluid_alsa_midi_run
  */
-void
+fluid_thread_return_t
 fluid_alsa_midi_run(void* d)
 {
   fluid_midi_event_t* evt;
@@ -706,6 +710,8 @@ fluid_alsa_midi_run(void* d)
       }
     }
   }
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 /**************************************************************
@@ -953,7 +959,7 @@ delete_fluid_alsa_seq_driver(fluid_midi_driver_t* p)
 /*
  * fluid_alsa_seq_run
  */
-void
+fluid_thread_return_t
 fluid_alsa_seq_run(void* d)
 {
   int n, ev;
@@ -1046,6 +1052,8 @@ fluid_alsa_seq_run(void* d)
 	while (ev > 0);
     }	/* if poll() > 0 */
   }	/* while (!dev->should_quit) */
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 #endif /* #if ALSA_SUPPORT */
diff --git a/src/drivers/fluid_oss.c b/src/drivers/fluid_oss.c
index 40683a94..05629da6 100644
--- a/src/drivers/fluid_oss.c
+++ b/src/drivers/fluid_oss.c
@@ -77,8 +77,8 @@ int delete_fluid_oss_audio_driver(fluid_audio_driver_t* p);
 
 /* local utilities */
 static int fluid_oss_set_queue_size(fluid_oss_audio_driver_t* dev, int ss, int ch, int qs, int bs);
-static void fluid_oss_audio_run(void* d);
-static void fluid_oss_audio_run2(void* d);
+static fluid_thread_return_t fluid_oss_audio_run(void* d);
+static fluid_thread_return_t fluid_oss_audio_run2(void* d);
 
 
 typedef struct {
@@ -95,7 +95,7 @@ new_fluid_oss_midi_driver(fluid_settings_t* settings,
 			 handle_midi_event_func_t handler, void* data);
 int delete_fluid_oss_midi_driver(fluid_midi_driver_t* p);
 int fluid_oss_midi_driver_status(fluid_midi_driver_t* p);
-static void fluid_oss_midi_run(void* d);
+static fluid_thread_return_t fluid_oss_midi_run(void* d);
 
 
 void
@@ -441,7 +441,7 @@ fluid_oss_set_queue_size(fluid_oss_audio_driver_t* dev, int ss, int ch, int qs,
 /*
  * fluid_oss_audio_run
  */
-void
+fluid_thread_return_t
 fluid_oss_audio_run(void* d)
 {
   fluid_oss_audio_driver_t* dev = (fluid_oss_audio_driver_t*) d;
@@ -463,13 +463,15 @@ fluid_oss_audio_run(void* d)
   }
 
   FLUID_LOG(FLUID_DBG, "Audio thread finished");
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 
 /*
  * fluid_oss_audio_run
  */
-void
+fluid_thread_return_t
 fluid_oss_audio_run2(void* d)
 {
   fluid_oss_audio_driver_t* dev = (fluid_oss_audio_driver_t*) d;
@@ -498,6 +500,8 @@ fluid_oss_audio_run2(void* d)
   }
 
   FLUID_LOG(FLUID_DBG, "Audio thread finished");
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 
@@ -621,7 +625,7 @@ delete_fluid_oss_midi_driver(fluid_midi_driver_t* p)
 /*
  * fluid_oss_midi_run
  */
-void
+fluid_thread_return_t
 fluid_oss_midi_run(void* d)
 {
   fluid_oss_midi_driver_t* dev = (fluid_oss_midi_driver_t*) d;
@@ -668,6 +672,8 @@ fluid_oss_midi_run(void* d)
       }
     }
   }
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 int
diff --git a/src/drivers/fluid_pulse.c b/src/drivers/fluid_pulse.c
index 9f939346..4ea00621 100644
--- a/src/drivers/fluid_pulse.c
+++ b/src/drivers/fluid_pulse.c
@@ -55,8 +55,8 @@ fluid_audio_driver_t* new_fluid_pulse_audio_driver2(fluid_settings_t* settings,
 						    fluid_audio_func_t func, void* data);
 int delete_fluid_pulse_audio_driver(fluid_audio_driver_t* p);
 void fluid_pulse_audio_driver_settings(fluid_settings_t* settings);
-static void fluid_pulse_audio_run(void* d);
-static void fluid_pulse_audio_run2(void* d);
+static fluid_thread_return_t fluid_pulse_audio_run(void* d);
+static fluid_thread_return_t fluid_pulse_audio_run2(void* d);
 
 
 void fluid_pulse_audio_driver_settings(fluid_settings_t* settings)
@@ -196,7 +196,7 @@ int delete_fluid_pulse_audio_driver(fluid_audio_driver_t* p)
 }
 
 /* Thread without audio callback, more efficient */
-static void
+static fluid_thread_return_t
 fluid_pulse_audio_run(void* d)
 {
   fluid_pulse_audio_driver_t* dev = (fluid_pulse_audio_driver_t*) d;
@@ -212,7 +212,7 @@ fluid_pulse_audio_run(void* d)
   if (buf == NULL)
   {
     FLUID_LOG(FLUID_ERR, "Out of memory.");
-    return;
+    return FLUID_THREAD_RETURN_VALUE;
   }
 
   while (dev->cont)
@@ -228,9 +228,11 @@ fluid_pulse_audio_run(void* d)
   }	/* while (dev->cont) */
 
   FLUID_FREE(buf);
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
-static void
+static fluid_thread_return_t
 fluid_pulse_audio_run2(void* d)
 {
   fluid_pulse_audio_driver_t* dev = (fluid_pulse_audio_driver_t*) d;
@@ -254,7 +256,7 @@ fluid_pulse_audio_run2(void* d)
     FLUID_FREE(right);
     FLUID_FREE(buf);
     FLUID_LOG(FLUID_ERR, "Out of memory.");
-    return;
+    return FLUID_THREAD_RETURN_VALUE;
   }
 
   handle[0] = left;
@@ -282,4 +284,6 @@ fluid_pulse_audio_run2(void* d)
   FLUID_FREE(left);
   FLUID_FREE(right);
   FLUID_FREE(buf);
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
diff --git a/src/drivers/fluid_winmidi.c b/src/drivers/fluid_winmidi.c
index b7c4bf45..73f7795e 100644
--- a/src/drivers/fluid_winmidi.c
+++ b/src/drivers/fluid_winmidi.c
@@ -76,7 +76,7 @@ int delete_fluid_winmidi_driver(fluid_midi_driver_t* p);
 
 void CALLBACK fluid_winmidi_callback(HMIDIIN hmi, UINT wMsg, DWORD_PTR dwInstance,
 				    DWORD_PTR msg, DWORD_PTR extra);
-static void fluid_winmidi_add_sysex_thread (void *data);
+static fluid_thread_return_t fluid_winmidi_add_sysex_thread (void *data);
 static char* fluid_winmidi_input_error(int no);
 int fluid_winmidi_driver_status(fluid_midi_driver_t* p);
 
@@ -339,7 +339,7 @@ fluid_winmidi_callback(HMIDIIN hmi, UINT wMsg, DWORD_PTR dwInstance,
 }
 
 /* Thread for re-adding SYSEX buffers */
-static void
+static fluid_thread_return_t
 fluid_winmidi_add_sysex_thread (void *data)
 {
   fluid_winmidi_driver_t *dev = data;
@@ -360,6 +360,8 @@ fluid_winmidi_add_sysex_thread (void *data)
       }
     }
   }
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 int
diff --git a/src/rvoice/fluid_rvoice_mixer.c b/src/rvoice/fluid_rvoice_mixer.c
index 1192d46a..4cde3628 100644
--- a/src/rvoice/fluid_rvoice_mixer.c
+++ b/src/rvoice/fluid_rvoice_mixer.c
@@ -715,7 +715,7 @@ fluid_mixer_get_mt_rvoice(fluid_rvoice_mixer_t* mixer)
 #define THREAD_BUF_TERMINATE 3
 
 /* Core thread function (processes voices in parallel to primary synthesis thread) */
-static void
+static fluid_thread_return_t
 fluid_mixer_thread_func (void* data)
 {
   fluid_mixer_buffers_t* buffers = data;  
@@ -756,6 +756,7 @@ fluid_mixer_thread_func (void* data)
     }
   }
 
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 static void
diff --git a/src/utils/fluid_sys.c b/src/utils/fluid_sys.c
index 6f23c3d3..f308de2b 100644
--- a/src/utils/fluid_sys.c
+++ b/src/utils/fluid_sys.c
@@ -661,7 +661,7 @@ fluid_thread_join(fluid_thread_t* thread)
 }
 
 
-void
+fluid_thread_return_t
 fluid_timer_run (void *data)
 {
   fluid_timer_t *timer;
@@ -694,7 +694,7 @@ fluid_timer_run (void *data)
   if (timer->auto_destroy)
     FLUID_FREE (timer);
 
-  return;
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 fluid_timer_t*
@@ -959,7 +959,7 @@ void fluid_socket_close(fluid_socket_t sock)
     close (sock);
 }
 
-static void
+static fluid_thread_return_t
 fluid_server_socket_run (void *data)
 {
   fluid_server_socket_t *server_socket = (fluid_server_socket_t *)data;
@@ -989,7 +989,7 @@ fluid_server_socket_run (void *data)
 	FLUID_LOG(FLUID_ERR, "Failed to accept connection");
 
       server_socket->cont = 0;
-      return;
+      return FLUID_THREAD_RETURN_VALUE;
     } else {
 #ifdef HAVE_INETNTOP
 #ifdef IPV6_SUPPORT
@@ -1012,6 +1012,8 @@ fluid_server_socket_run (void *data)
   }
 
   FLUID_LOG(FLUID_DBG, "Server closing");
+
+  return FLUID_THREAD_RETURN_VALUE;
 }
 
 fluid_server_socket_t*
@@ -1122,7 +1124,7 @@ void fluid_socket_close (fluid_socket_t sock)
     closesocket (sock);
 }
 
-static void fluid_server_socket_run (void *data)
+static fluid_thread_return_t fluid_server_socket_run (void *data)
 {
   fluid_server_socket_t *server_socket = (fluid_server_socket_t *)data;
   fluid_socket_t client_socket;
@@ -1153,7 +1155,7 @@ static void fluid_server_socket_run (void *data)
 	FLUID_LOG (FLUID_ERR, "Failed to accept connection: %ld", WSAGetLastError ());
 
       server_socket->cont = 0;
-      return;
+      return FLUID_THREAD_RETURN_VALUE;
     }
     else
     {
@@ -1177,6 +1179,8 @@ static void fluid_server_socket_run (void *data)
   }
 
   FLUID_LOG (FLUID_DBG, "Server closing");
+  
+  return FLUID_THREAD_RETURN_VALUE;  
 }
 
 fluid_server_socket_t*
diff --git a/src/utils/fluid_sys.h b/src/utils/fluid_sys.h
index 36867645..6e58ae69 100644
--- a/src/utils/fluid_sys.h
+++ b/src/utils/fluid_sys.h
@@ -291,8 +291,13 @@ fluid_atomic_float_get(volatile float *fptr)
 
 /* Threads */
 
+/* other thread implementations might change this for their needs */
+typedef void* fluid_thread_return_t;
+/* static return value for thread functions which requires a return value */
+#define FLUID_THREAD_RETURN_VALUE (NULL)
+
 typedef GThread fluid_thread_t;
-typedef void (*fluid_thread_func_t)(void* data);
+typedef fluid_thread_return_t (*fluid_thread_func_t)(void* data);
 
 #define FLUID_THREAD_ID_NULL            NULL                    /* A NULL "ID" value */
 #define fluid_thread_id_t               GThread *               /* Data type for a thread ID */