diff --git a/src/charset.c b/src/charset.c
index cdb9e48..d649179 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -1733,6 +1733,8 @@
 	if (enc_latin1like)
 	    return latin1upper[c];
     }
+    if (c < 0x80 && (cmp_flags & CMP_KEEPASCII))
+	return TOUPPER_ASC(c);
     return TOUPPER_LOC(c);
 }
 
@@ -1757,6 +1759,8 @@
 	if (enc_latin1like)
 	    return latin1lower[c];
     }
+    if (c < 0x80 && (cmp_flags & CMP_KEEPASCII))
+	return TOLOWER_ASC(c);
     return TOLOWER_LOC(c);
 }
 #endif