diff --git a/posix/wordexp.c b/posix/wordexp.c
index 36b6fff..661dfd4 100644
--- a/posix/wordexp.c
+++ b/posix/wordexp.c
@@ -1218,6 +1218,9 @@ parse_comm (char **word, size_t *word_length, size_t *max_length,
   return WRDE_SYNTAX;
 }
 
+#define CHAR_IN_SET(ch, char_set) \
+  (memchr (char_set "", (ch), sizeof (char_set) - 1) != NULL)
+
 static int
 internal_function
 parse_param (char **word, size_t *word_length, size_t *max_length,
@@ -1299,7 +1302,7 @@ parse_param (char **word, size_t *word_length, size_t *max_length,
 	}
       while (isdigit(words[++*offset]));
     }
-  else if (words[*offset] != '\0' && strchr ("*@$", words[*offset]) != NULL)
+  else if (CHAR_IN_SET (words[*offset], "*@$"))
     {
       /* Special parameter. */
       special = 1;
@@ -1343,8 +1346,7 @@ parse_param (char **word, size_t *word_length, size_t *max_length,
 	  break;
 
 	case ':':
-	  if (words[1 + *offset] == '\0'
-	      || strchr ("-=?+", words[1 + *offset]) == NULL)
+	  if (!CHAR_IN_SET (words[1 + *offset], "-=?+"))
 	    goto syntax;
 
 	  colon_seen = 1;
@@ -2046,6 +2048,8 @@ do_error:
   return error;
 }
 
+#undef CHAR_IN_SET
+
 static int
 internal_function
 parse_dollars (char **word, size_t *word_length, size_t *max_length,