diff --git a/modules/src/string/str2bts.c b/modules/src/string/str2bts.c
index 566183118..4b9abd0b7 100644
--- a/modules/src/string/str2bts.c
+++ b/modules/src/string/str2bts.c
@@ -9,8 +9,7 @@ static
 is_oct(c)
 	char c;
 {
-	return (c == '0' || c == '1' || c == '2' || c == '3' ||
-		c == '4' || c == '5' || c == '6' || c == '7');
+	return ((unsigned int)(c-'0') <= ('7'-'0'));
 }
 
 /*	str2bts() strips the escaped characters of a
diff --git a/modules/src/string/str2long.c b/modules/src/string/str2long.c
index 208d52c07..294042496 100644
--- a/modules/src/string/str2long.c
+++ b/modules/src/string/str2long.c
@@ -10,12 +10,14 @@ value(c, b)
 	char c;
 	int b;
 {
-	if (c >= '0' && c <= '9')
-		return c - '0';
-	if (c >= 'A' && c <= 'F')
-		return c - 'A' + 10;
-	if (c >= 'a' && c <= 'f')
-		return c - 'a' + 10;
+	register int ch;
+
+	ch = c - '0';
+	if ((unsigned) ch <= 9) return ch;
+	ch = c - 'A';
+	if ((unsigned) ch <= 5) return ch + 10;
+	ch = c - 'a';
+	if ((unsigned) ch <= 5) return ch + 10;
 	return b;
 }