diff --git a/bin/sh/histedit.c b/bin/sh/histedit.c
index a8c376a295f..c65d1c7134e 100644
--- a/bin/sh/histedit.c
+++ b/bin/sh/histedit.c
@@ -166,9 +166,10 @@ sethistsize(const char *hs)
 	HistEvent he;
 
 	if (hist != NULL) {
-		if (hs == NULL || *hs == '\0' ||
-		   (histsize = atoi(hs)) < 0)
+		if (hs == NULL || !is_number(hs))
 			histsize = 100;
+		else
+			histsize = atoi(hs);
 		history(hist, &he, H_SETSIZE, histsize);
 		history(hist, &he, H_SETUNIQUE, 1);
 	}