diff --git a/src/ops.c b/src/ops.c
index 46101a4..f6d765b 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -2734,7 +2734,7 @@
 	{
 	    if (CharOrd(firstdigit) < Prenum1)
 	    {
-		if (isupper(firstdigit))
+		if (SAFE_isupper(firstdigit))
 		    firstdigit = 'A';
 		else
 		    firstdigit = 'a';
@@ -2746,7 +2746,7 @@
 	{
 	    if (26 - CharOrd(firstdigit) - 1 < Prenum1)
 	    {
-		if (isupper(firstdigit))
+		if (SAFE_isupper(firstdigit))
 		    firstdigit = 'Z';
 		else
 		    firstdigit = 'z';
@@ -2875,9 +2875,9 @@
 	save_pos = curwin->w_cursor;
 	for (i = 0; i < todel; ++i)
 	{
-	    if (c < 0x100 && isalpha(c))
+	    if (c < 0x100 && SAFE_isalpha(c))
 	    {
-		if (isupper(c))
+		if (SAFE_isupper(c))
 		    hexupper = TRUE;
 		else
 		    hexupper = FALSE;