diff --git a/src/lisp.h b/src/lisp.h
index e0bad58f758..daf57ed906f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1371,8 +1371,9 @@ STRING_SET_CHARS (Lisp_Object string, ptrdiff_t newsize)
 {
   /* This function cannot change the size of data allocated for the
      string when it was created.  */
-  eassert ((STRING_MULTIBYTE (string) && newsize <= SBYTES (string))
-	   || (!STRING_MULTIBYTE (string) && newsize == SCHARS (string)));
+  eassert (STRING_MULTIBYTE (string)
+	   ? newsize <= SBYTES (string)
+	   : newsize == SCHARS (string));
   XSTRING (string)->size = newsize;
 }