diff --git a/src/Makefile.mingw b/src/Makefile.mingw
index 76c61c83b..2b4536436 100644
--- a/src/Makefile.mingw
+++ b/src/Makefile.mingw
@@ -132,6 +132,7 @@ endif
 
 
 ifeq ($(WALTJE), y)
+OPENDIR = win_opendir.o
 SERIAL	= serial.o
 WSERIAL = win_serial.o
 WFLAGS	= -DWALTJE
@@ -241,7 +242,7 @@ VIDOBJ	= video.o \
 WINOBJ	= win.o \
 	  win_ddraw.o win_ddraw_fs.o win_ddraw_screenshot.o \
 	  win_d3d.o win_d3d_fs.o \
-	  win_language.o win_status.o win_opendir.o win_dynld.o \
+	  win_language.o win_status.o $(OPENDIR) win_dynld.o \
 	  win_video.o $(WSERIAL) win_keyboard.o win_mouse.o \
 	  win_iodev.o win_joystick.o win_midi.o \
 	  win_settings.o win_deviceconfig.o win_joystickconfig.o \
diff --git a/src/WIN/win_language.c b/src/WIN/win_language.c
index ed4e19159..84eabd1b7 100644
--- a/src/WIN/win_language.c
+++ b/src/WIN/win_language.c
@@ -198,7 +198,7 @@ int file_dlg_w(HWND hwnd, WCHAR *f, WCHAR *fn, int save)
 	}
         if (r)
         {
-		wcstombs(openfilestring, wopenfilestring, 520);
+		wcstombs(openfilestring, wopenfilestring, sizeof(openfilestring));
                 pclog("File dialog return true\n");
                 return 0;
         }
diff --git a/src/WIN/win_settings.c b/src/WIN/win_settings.c
index 6bcaab48f..6000827be 100644
--- a/src/WIN/win_settings.c
+++ b/src/WIN/win_settings.c
@@ -663,7 +663,7 @@ static BOOL CALLBACK win_settings_machine_proc(HWND hdlg, UINT message, WPARAM w
 
 			h = GetDlgItem(hdlg, IDC_MEMTEXT);
 			SendMessage(h, WM_GETTEXT, 255, (LPARAM) lptsTemp);
-			wcstombs(stransi, lptsTemp, (wcslen(lptsTemp) * 2) + 2);
+			wcstombs(stransi, lptsTemp, sizeof(stransi));
 			sscanf(stransi, "%i", &temp_mem_size);
 			temp_mem_size &= ~(models[temp_model].ram_granularity - 1);
 			if (temp_mem_size < models[temp_model].min_ram)
@@ -765,7 +765,7 @@ static BOOL CALLBACK win_settings_video_proc(HWND hdlg, UINT message, WPARAM wPa
 
                         h = GetDlgItem(hdlg, IDC_COMBO_VIDEO);
                         SendMessage(h, CB_GETLBTEXT, SendMessage(h, CB_GETCURSEL, 0, 0), (LPARAM) lptsTemp);
-			wcstombs(stransi, lptsTemp, (wcslen(lptsTemp) * 2) + 2);
+			wcstombs(stransi, lptsTemp, sizeof(stransi));
 			gfx = video_card_getid(stransi);
 
 			h = GetDlgItem(hdlg, IDC_CONFIGURE_VID);
@@ -792,7 +792,7 @@ static BOOL CALLBACK win_settings_video_proc(HWND hdlg, UINT message, WPARAM wPa
 
 		                        h = GetDlgItem(hdlg, IDC_COMBO_VIDEO);
 		                        SendMessage(h, CB_GETLBTEXT, SendMessage(h, CB_GETCURSEL, 0, 0), (LPARAM) lptsTemp);
-					wcstombs(stransi, lptsTemp, (wcslen(lptsTemp) * 2) + 2);
+					wcstombs(stransi, lptsTemp, sizeof(stransi));
 					gfx = video_card_getid(stransi);
 		                        temp_gfxcard = video_new_to_old(gfx);
 
@@ -828,7 +828,7 @@ static BOOL CALLBACK win_settings_video_proc(HWND hdlg, UINT message, WPARAM wPa
 
 					h = GetDlgItem(hdlg, IDC_COMBO_VIDEO);
 		                        SendMessage(h, CB_GETLBTEXT, SendMessage(h, CB_GETCURSEL, 0, 0), (LPARAM) lptsTemp);
-					wcstombs(stransi, lptsTemp, (wcslen(lptsTemp) * 2) + 2);
+					wcstombs(stransi, lptsTemp, sizeof(stransi));
 					deviceconfig_open(hdlg, (void *)video_card_getdevice(video_card_getid(stransi)));
 
 					free(stransi);
@@ -843,7 +843,7 @@ static BOOL CALLBACK win_settings_video_proc(HWND hdlg, UINT message, WPARAM wPa
 
                         h = GetDlgItem(hdlg, IDC_COMBO_VIDEO);
                         SendMessage(h, CB_GETLBTEXT, SendMessage(h, CB_GETCURSEL, 0, 0), (LPARAM) lptsTemp);
-			wcstombs(stransi, lptsTemp, (wcslen(lptsTemp) * 2) + 2);
+			wcstombs(stransi, lptsTemp, sizeof(stransi));
                         temp_gfxcard = video_new_to_old(video_card_getid(stransi));
 
                         h = GetDlgItem(hdlg, IDC_COMBO_VIDEO_SPEED);
@@ -2436,7 +2436,7 @@ static void get_edit_box_contents(HWND hdlg, int id, uint64_t *val)
 
 	h = GetDlgItem(hdlg, id);
 	SendMessage(h, WM_GETTEXT, 255, (LPARAM) szText);
-	wcstombs(stransi, szText, (wcslen(szText) * 2) + 2);
+	wcstombs(stransi, szText, sizeof(stransi));
 	sscanf(stransi, "%" PRIu64, val);
 }
 
diff --git a/src/cdrom_image.cc b/src/cdrom_image.cc
index 204708742..a7fee4477 100644
--- a/src/cdrom_image.cc
+++ b/src/cdrom_image.cc
@@ -985,7 +985,7 @@ int image_open(uint8_t id, wchar_t *fn)
 	}
 
         cdimg[id] = new CDROM_Interface_Image();
-	wcstombs(afn, fn, (wcslen(fn) << 1) + 2);
+	wcstombs(afn, fn, sizeof(afn));
         if (!cdimg[id]->SetDevice(afn, false))
         {
                 image_close(id);
diff --git a/src/config.c b/src/config.c
index e59225fed..9821b3f5a 100644
--- a/src/config.c
+++ b/src/config.c
@@ -225,7 +225,7 @@ int config_load(wchar_t *fn)
                         strncpy(new_entry->name, ename, 256);
 			memcpy(new_entry->wdata, &cfgbuffer[data_pos], 512);
 			new_entry->wdata[255] = L'\0';
-			wcstombs(new_entry->data, new_entry->wdata, 512);
+			wcstombs(new_entry->data, new_entry->wdata, sizeof(new_entry->data));
 			new_entry->data[255] = '\0';
                         list_add(&new_entry->list, &current_section->entry_head);
                 }