diff --git a/degesch.c b/degesch.c
index ea93fdf..3b1bc9a 100644
--- a/degesch.c
+++ b/degesch.c
@@ -5134,9 +5134,11 @@ utf8_common_prefix (const char **vector, size_t len)
 	{
 		for (size_t i = 1; i < len; i++)
 		{
-			// Not bothering with lowercasing non-ASCII
 			int32_t other = utf8_iter_next (&a[i], NULL);
-			if (other < 0 || ch >= 0x80 || other >= 0x80
+			if (ch == other)
+				continue;
+			// Not bothering with lowercasing non-ASCII
+			if (ch >= 0x80 || other >= 0x80
 			 || tolower_ascii (ch) != tolower_ascii (other))
 				return prefix;
 		}