diff --git a/quote.c b/quote.c
index 24a58ba..bcc0dbc 100644
--- a/quote.c
+++ b/quote.c
@@ -55,7 +55,7 @@
 	}
 
 	for (p = src; *p; p++) {
-		if (!isalpha(*p) && !isdigit(*p) && !strchr(ok_punct, *p)) {
+		if (!isalnum(*p) && !strchr(ok_punct, *p)) {
 			sq_quote_buf(dst, src);
 			return;
 		}