diff --git a/charset.c b/charset.c
index 9e6fec78..bb58d8df 100644
--- a/charset.c
+++ b/charset.c
@@ -571,14 +571,7 @@ utf_bin_count(data, len)
 	{
 		if (is_utf8_well_formed(data, edata-data))
 		{
-			LWCHAR c = step_char(&data, +1, edata);
-			if (ctldisp == OPT_ONPLUS && IS_CSI_START(c))
-			{
-				do {
-					c = step_char(&data, +1, edata);
-				} while (data < edata && is_ansi_middle(c));
-			}
-			if (binary_char(c))
+			if (bin_char_in_string(&data, edata))
 				bin_count++;
 		} else /* invalid UTF-8 */
 		{
diff --git a/filename.c b/filename.c
index cbc7e0ee..c519c591 100644
--- a/filename.c
+++ b/filename.c
@@ -477,13 +477,7 @@ bin_file(f)
 		pend = &data[n];
 		for (p = data;  p < pend;  )
 		{
-			LWCHAR c = step_char(&p, +1, pend);
-			if (ctldisp == OPT_ONPLUS && IS_CSI_START(c))
-			{
-				do {
-					c = step_char(&p, +1, pend);
-				} while (p < pend && is_ansi_middle(c));
-			} else if (binary_char(c))
+			if (bin_char_in_string(&p, pend))
 				bin_count++;
 		}
 	}
@@ -494,6 +488,26 @@ bin_file(f)
 	return (bin_count > 5);
 }
 
+/*
+ * Determine if the next char in a string is binary.
+ */
+	public int
+bin_char_in_string(pp, limit)
+	char **pp;
+	constant char *limit;
+{
+	LWCHAR c = step_char(pp, +1, limit);
+	if (ctldisp == OPT_ONPLUS && IS_CSI_START(c))
+	{
+		/* Skip the CSI sequence. */
+		do {
+			c = step_char(pp, +1, limit);
+		} while (*pp < limit && is_ansi_middle(c));
+	} else if (binary_char(c))
+		return (1);
+	return (0);
+}
+
 /*
  * Try to determine the size of a file by seeking to the end.
  */