diff --git a/libbb/xgetlarg.c b/libbb/xgetlarg.c
index 0460aad57..f24492bee 100644
--- a/libbb/xgetlarg.c
+++ b/libbb/xgetlarg.c
@@ -21,8 +21,10 @@ extern long bb_xgetlarg(const char *arg, int base, long lower, long upper)
 
 	assert(arg!=NULL);
 
-	/* Don't allow leading whitespace. */
-	if (isspace(*arg)) {	/* Use an actual function call for minimal size. */
+	/* Don't allow leading whitespace.
+	 * Wrap isspace in () to make sure we call the 
+	 * function rather than the macro. */
+	if ((isspace)(*arg)) {
 		bb_show_usage();
 	}