diff --git a/ldiscucs.c b/ldiscucs.c
index 6c943a09..50ce2094 100644
--- a/ldiscucs.c
+++ b/ldiscucs.c
@@ -84,7 +84,7 @@ void luni_send(Ldisc *ldisc, const wchar_t *widebuf, int len, int interactive)
     } else {
 	int rv;
 	rv = wc_to_mb(ldisc->term->ucsdata->line_codepage, 0, widebuf, len,
-		      linebuffer, linesize, NULL, NULL, ldisc->term->ucsdata);
+		      linebuffer, linesize, NULL, ldisc->term->ucsdata);
 	if (rv >= 0)
 	    p = linebuffer + rv;
 	else
diff --git a/putty.h b/putty.h
index aa82890f..242bfa67 100644
--- a/putty.h
+++ b/putty.h
@@ -1294,7 +1294,7 @@ int is_dbcs_leadbyte(int codepage, char byte);
 int mb_to_wc(int codepage, int flags, const char *mbstr, int mblen,
 	     wchar_t *wcstr, int wclen);
 int wc_to_mb(int codepage, int flags, const wchar_t *wcstr, int wclen,
-	     char *mbstr, int mblen, const char *defchr, int *defused,
+	     char *mbstr, int mblen, const char *defchr,
 	     struct unicode_data *ucsdata);
 wchar_t xlat_uskbd2cyrllic(int ch);
 int check_compose(int first, int second);
diff --git a/unix/gtkfont.c b/unix/gtkfont.c
index d0ecaa96..c2a610f1 100644
--- a/unix/gtkfont.c
+++ b/unix/gtkfont.c
@@ -595,7 +595,7 @@ static int x11font_has_glyph(unifont *font, wchar_t glyph)
          */
         char sbstring[2];
         int sblen = wc_to_mb(xfont->real_charset, 0, &glyph, 1,
-                             sbstring, 2, "", NULL, NULL);
+                             sbstring, 2, "", NULL);
         if (sblen == 0 || !sbstring[0])
             return FALSE;              /* not even in the charset */
 
@@ -950,7 +950,7 @@ static void x11font_draw_text(unifont_drawctx *ctx, unifont *font,
          */
         char *sbstring = snewn(len+1, char);
         int sblen = wc_to_mb(xfont->real_charset, 0, string, len,
-                             sbstring, len+1, ".", NULL, NULL);
+                             sbstring, len+1, ".", NULL);
 	x11font_really_draw_text(x11font_drawfuncs + index + 0, ctx,
                                  &xfont->fonts[sfid], xfont->disp, x, y,
 				 sbstring, sblen, shadowoffset,
@@ -1631,7 +1631,7 @@ static void pangofont_draw_internal(unifont_drawctx *ctx, unifont *font,
      */
     utfstring = snewn(len*6+1, char); /* UTF-8 has max 6 bytes/char */
     utflen = wc_to_mb(CS_UTF8, 0, string, len,
-                      utfstring, len*6+1, ".", NULL, NULL);
+                      utfstring, len*6+1, ".", NULL);
 
     utfptr = utfstring;
     while (utflen > 0) {
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index ec53b6c8..64aae476 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -3049,7 +3049,7 @@ void write_clip(Frontend *inst, int clipboard,
     state->pasteout_data_len = wc_to_mb(inst->ucsdata.line_codepage, 0,
 				       data, len, state->pasteout_data,
 				       state->pasteout_data_len,
-				       NULL, NULL, NULL);
+				       NULL, NULL);
     if (state->pasteout_data_len == 0) {
 	sfree(state->pasteout_data);
 	state->pasteout_data = NULL;
diff --git a/unix/uxucs.c b/unix/uxucs.c
index 86cc33d4..edaca92c 100644
--- a/unix/uxucs.c
+++ b/unix/uxucs.c
@@ -57,13 +57,9 @@ int mb_to_wc(int codepage, int flags, const char *mbstr, int mblen,
 }
 
 int wc_to_mb(int codepage, int flags, const wchar_t *wcstr, int wclen,
-	     char *mbstr, int mblen, const char *defchr, int *defused,
+	     char *mbstr, int mblen, const char *defchr,
 	     struct unicode_data *ucsdata)
 {
-    /* FIXME: we should remove the defused param completely... */
-    if (defused)
-	*defused = 0;
-
     if (codepage == DEFAULT_CODEPAGE) {
 	char output[MB_LEN_MAX];
 	mbstate_t state;
diff --git a/windows/winucs.c b/windows/winucs.c
index 0ecd225e..f40444c9 100644
--- a/windows/winucs.c
+++ b/windows/winucs.c
@@ -1157,7 +1157,7 @@ void get_unitab(int codepage, wchar_t * unitab, int ftype)
 }
 
 int wc_to_mb(int codepage, int flags, const wchar_t *wcstr, int wclen,
-	     char *mbstr, int mblen, const char *defchr, int *defused,
+	     char *mbstr, int mblen, const char *defchr,
 	     struct unicode_data *ucsdata)
 {
     char *p;
@@ -1180,7 +1180,6 @@ int wc_to_mb(int codepage, int flags, const wchar_t *wcstr, int wclen,
 		int j;
 		for (j = 0; defchr[j]; j++)
 		    *p++ = defchr[j];
-		if (defused) *defused = 1;
 	    }
 #if 1
 	    else
@@ -1189,9 +1188,11 @@ int wc_to_mb(int codepage, int flags, const wchar_t *wcstr, int wclen,
 	    assert(p - mbstr < mblen);
 	}
 	return p - mbstr;
-    } else
+    } else {
+        int defused;
 	return WideCharToMultiByte(codepage, flags, wcstr, wclen,
-				   mbstr, mblen, defchr, defused);
+				   mbstr, mblen, defchr, &defused);
+    }
 }
 
 int mb_to_wc(int codepage, int flags, const char *mbstr, int mblen,