diff --git a/mime.c b/mime.c

index 45de80a..ecac85d 100644

--- a/mime.c

+++ b/mime.c

@@ -1109,16 +1109,34 @@ fromhdr_end:

 }

 /*

+ * return length of this UTF-8 codepoint in bytes

+ */

+static size_t

+codepointsize(char tc)

+{

+	int rv = 0;

+	if ( ! ( tc & 0x80 ) )

+		return 1;

+	while ( tc & 0x80 )

+	{

+		rv++;

+		tc = tc<<1;

+	}

+	return rv;

+}

+

+/*

  * Convert header fields to RFC 1522 format and write to the file fo.

  */

 static size_t

 mime_write_tohdr(struct str *in, FILE *fo)

 {

 	char *upper, *wbeg, *wend, *charset, *lastwordend = NULL, *lastspc, b,

-		*charset7;

+		*charset7, *cp;

 	struct str cin, cout;

-	size_t sz = 0, col = 0, wr, charsetlen, charset7len;

+	size_t sz = 0, col = 0, wr, charsetlen, charset7len, cpsz;

 	int quoteany, mustquote, broken,

+		maxin, maxout, curin, cps,

 		maxcol = 65 /* there is the header field's name, too */;

 	upper = in->s + in->l;

@@ -1134,41 +1152,75 @@ mime_write_tohdr(struct str *in, FILE *fo)

 		if (mustquote_hdr(wbeg, wbeg == in->s, wbeg == &upper[-1]))

 			quoteany++;

 	}

+

+	/*

+	 * rfc2047 says we cannot split multi-byte characters over

+	 * encoded words, so we need to know if we're a multi-byte

+	 * source stream (UTF-8 specifically) or just an 8 bit

+	 * stream like ISO-8859-15

+	 * so test beginning of charset since it is valid to include

+	 * language in charset "UTF-8*DE" etc as per rfc 2184/2231

+	 */

+	char *thisset = b&0200 ? charset : charset7;

+	int is_utf8 = ( strncasecmp( thisset, "utf-8", 5 ) == 0 );

+

 	if (2 * quoteany > in->l) {

 		/*

 		 * Print the entire field in base64.

 		 */

-		for (wbeg = in->s; wbeg < upper; wbeg = wend) {

+		for (wbeg = in->s; wbeg < upper; ) {

 			wend = upper;

 			cin.s = wbeg;

-			for (;;) {

-				cin.l = wend - wbeg;

-				if (cin.l * 4/3 + 7 + charsetlen

-						< maxcol - col) {

-					fprintf(fo, "=?%s?B?",

-						b&0200 ? charset : charset7);

-					wr = mime_write_tob64(&cin, fo, 1);

-					fwrite("?=", sizeof (char), 2, fo);

-					wr += 7 + charsetlen;

-					sz += wr, col += wr;

-					if (wend < upper) {

-						fwrite("\n ", sizeof (char),

-								2, fo);

-						sz += 2;

-						col = 0;

-						maxcol = 76;

+			/*

+			 * we calculate the maximum number of bytes

+			 * we can use on this output line, and then what

+			 * this equates to as base64 encoded source bytes

+			 */

+			maxout = maxcol - col - 7 - charsetlen;

+			maxin = (maxout - (maxout & 0x03)) * 3/4;

+

+			/* short enough to finish ? */

+			if (maxin > upper - wbeg )

+			{

+				curin = upper - wbeg;

+				wbeg += curin;

+			}else

+			{

+				if (is_utf8)

+				{

+					/*

+					 * now scan the input from the beginning

+					 * to see how many codepoints will fit

+					 */

+					curin = 0;

+					while (curin < maxin

+						&& (cpsz = codepointsize(*wbeg)) <= (maxin - curin))

+					{

+						curin += cpsz;

+						wbeg += cpsz;

 					}

-					break;

-				} else {

-					if (col) {

-						fprintf(fo, "\n ");

-						sz += 2;

-						col = 0;

-						maxcol = 76;

-					} else

-						wend -= 4;

+				}else

+				{

+					curin = maxin;

+					wbeg += maxin;

 				}

 			}

+			cin.l = curin;

+			fprintf(fo, "%s=?%s?B?", (cin.s != in->s) ? " " : "", thisset );

+			wr = mime_write_tob64(&cin, fo, 1);

+

+			if (wbeg < upper)

+			{

+				wr += fwrite("?=\n ", sizeof (char), 4, fo) * sizeof (char);

+			}else

+			{

+				wr += fwrite("?=", sizeof (char), 2, fo) * sizeof (char);

+			}

+

+			/* and shuffle pointers and counts */

+			col = 1;

+			maxcol = 76;

+			sz += wr + 7 + charsetlen + ((cin.s != in->s) ? 1 : 0 );

 		}

 	} else {

 		/*

@@ -1243,7 +1295,29 @@ mime_write_tohdr(struct str *in, FILE *fo)

 								maxcol -= wbeg -

 									lastspc;

 						} else {

-							wend -= 4;

+							if (is_utf8)

+							{

+								/*

+								 * make sure wend is not pointing to

+								 * the middle of a codepoint

+								 */

+								cp = wend;

+								while (--cp > wbeg)

+								{

+									cps = codepointsize(*cp);

+									if (cps > 1)

+									{

+										if (wend - cp - cps > 4)

+											wend -= 4;

+										else

+											wend = cp;

+										break;

+									}

+								}

+								if (cp == wbeg)

+									wend -= 4;

+							} else

+								wend -= 4;

 						}

 						free(cout.s);

 					}