diff --git a/src/search.c b/src/search.c
index 246f9cbdf4d..3ba413ae8c2 100644
--- a/src/search.c
+++ b/src/search.c
@@ -221,6 +221,7 @@ compile_pattern (pattern, regp, translate, posix, multibyte)
       if (NILP (cp->regexp))
 	goto compile_it;
       if (XSTRING (cp->regexp)->size == XSTRING (pattern)->size
+	  && STRING_MULTIBYTE (cp->regexp) == STRING_MULTIBYTE (pattern)
 	  && !NILP (Fstring_equal (cp->regexp, pattern))
 	  && EQ (cp->buf.translate, (! NILP (translate) ? translate : make_number (0)))
 	  && cp->posix == posix