diff --git a/src/proto/spell.pro b/src/proto/spell.pro
index 6b1f84b..3f97008 100644
--- a/src/proto/spell.pro
+++ b/src/proto/spell.pro
@@ -27,7 +27,7 @@
 void init_spell_chartab(void);
 int spell_iswordp(char_u *p, win_T *wp);
 int spell_iswordp_nmw(char_u *p, win_T *wp);
-int spell_casefold(char_u *str, int len, char_u *buf, int buflen);
+int spell_casefold(win_T *wp, char_u *str, int len, char_u *buf, int buflen);
 int check_need_cap(linenr_T lnum, colnr_T col);
 void ex_spellrepall(exarg_T *eap);
 void onecap_copy(char_u *word, char_u *wcopy, int upper);
diff --git a/src/spell.c b/src/spell.c
index d430566..0b693c7 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -249,7 +249,7 @@
     if (*mi.mi_fend != NUL)
 	MB_PTR_ADV(mi.mi_fend);
 
-    (void)spell_casefold(ptr, (int)(mi.mi_fend - ptr), mi.mi_fword,
+    (void)spell_casefold(wp, ptr, (int)(mi.mi_fend - ptr), mi.mi_fword,
 							     MAXWLEN + 1);
     mi.mi_fwordlen = (int)STRLEN(mi.mi_fword);
 
@@ -736,7 +736,8 @@
 		    {
 			// "fword" is only needed for checking syllables.
 			if (ptr == mip->mi_word)
-			    (void)spell_casefold(ptr, wlen, fword, MAXWLEN);
+			    (void)spell_casefold(mip->mi_win,
+						    ptr, wlen, fword, MAXWLEN);
 			else
 			    vim_strncpy(fword, ptr, endlen[endidxcnt]);
 		    }
@@ -1213,7 +1214,7 @@
     if (*mip->mi_fend != NUL)
 	MB_PTR_ADV(mip->mi_fend);
 
-    (void)spell_casefold(p, (int)(mip->mi_fend - p),
+    (void)spell_casefold(mip->mi_win, p, (int)(mip->mi_fend - p),
 			     mip->mi_fword + mip->mi_fwordlen,
 			     MAXWLEN - mip->mi_fwordlen);
     flen = (int)STRLEN(mip->mi_fword + mip->mi_fwordlen);
@@ -2737,6 +2738,7 @@
  */
     int
 spell_casefold(
+    win_T	*wp,
     char_u	*str,
     int		len,
     char_u	*buf,
@@ -2765,7 +2767,21 @@
 		return FAIL;
 	    }
 	    c = mb_cptr2char_adv(&p);
-	    outi += mb_char2bytes(SPELL_TOFOLD(c), buf + outi);
+
+	    // Exception: greek capital sigma 0x03A3 folds to 0x03C3, except
+	    // when it is the last character in a word, then it folds to
+	    // 0x03C2.
+	    if (c == 0x03a3 || c == 0x03c2)
+	    {
+		if (p == str + len || !spell_iswordp(p, wp))
+		    c = 0x03c2;
+		else
+		    c = 0x03c3;
+	    }
+	    else
+		c = SPELL_TOFOLD(c);
+
+	    outi += mb_char2bytes(c, buf + outi);
 	}
 	buf[outi] = NUL;
     }
@@ -3097,7 +3113,8 @@
 	    word = inword;
 	else
 	{
-	    (void)spell_casefold(inword, (int)STRLEN(inword), fword, MAXWLEN);
+	    (void)spell_casefold(curwin,
+				  inword, (int)STRLEN(inword), fword, MAXWLEN);
 	    word = fword;
 	}
 
diff --git a/src/spellfile.c b/src/spellfile.c
index 2018169..264264c 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -3429,9 +3429,9 @@
     if (ga_grow(gap, 1) == OK)
     {
 	ftp = ((fromto_T *)gap->ga_data) + gap->ga_len;
-	(void)spell_casefold(from, (int)STRLEN(from), word, MAXWLEN);
+	(void)spell_casefold(curwin, from, (int)STRLEN(from), word, MAXWLEN);
 	ftp->ft_from = getroom_save(spin, word);
-	(void)spell_casefold(to, (int)STRLEN(to), word, MAXWLEN);
+	(void)spell_casefold(curwin, to, (int)STRLEN(to), word, MAXWLEN);
 	ftp->ft_to = getroom_save(spin, word);
 	++gap->ga_len;
     }
@@ -4391,7 +4391,7 @@
     int		res = OK;
     char_u	*p;
 
-    (void)spell_casefold(word, len, foldword, MAXWLEN);
+    (void)spell_casefold(curwin, word, len, foldword, MAXWLEN);
     for (p = pfxlist; res == OK; ++p)
     {
 	if (!need_affix || (p != NULL && *p != NUL))
diff --git a/src/spellsuggest.c b/src/spellsuggest.c
index 3de9ff2..2951eea 100644
--- a/src/spellsuggest.c
+++ b/src/spellsuggest.c
@@ -791,7 +791,7 @@
     if (su->su_badlen >= MAXWLEN)
 	su->su_badlen = MAXWLEN - 1;	// just in case
     vim_strncpy(su->su_badword, su->su_badptr, su->su_badlen);
-    (void)spell_casefold(su->su_badptr, su->su_badlen,
+    (void)spell_casefold(curwin, su->su_badptr, su->su_badlen,
 						    su->su_fbadword, MAXWLEN);
     // TODO: make this work if the case-folded text is longer than the original
     // text. Currently an illegal byte causes wrong pointer computations.
@@ -1176,7 +1176,7 @@
     STRCPY(fword, su->su_fbadword);
     n = (int)STRLEN(fword);
     p = su->su_badptr + su->su_badlen;
-    (void)spell_casefold(p, (int)STRLEN(p), fword + n, MAXWLEN - n);
+    (void)spell_casefold(curwin, p, (int)STRLEN(p), fword + n, MAXWLEN - n);
 
     for (lpi = 0; lpi < curwin->w_s->b_langp.ga_len; ++lpi)
     {
@@ -3005,7 +3005,8 @@
     else
     {
 	// soundfold the bad word with more characters following
-	(void)spell_casefold(su->su_badptr, stp->st_orglen, fword, MAXWLEN);
+	(void)spell_casefold(curwin,
+				su->su_badptr, stp->st_orglen, fword, MAXWLEN);
 
 	// When joining two words the sound often changes a lot.  E.g., "t he"
 	// sounds like "t h" while "the" sounds like "@".  Avoid that by
diff --git a/src/version.c b/src/version.c
index 25f2d15..99a635b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2974,
+/**/
     2973,
 /**/
     2972,