diff --git a/storage/innobase/handler/handler0alter.cc b/storage/innobase/handler/handler0alter.cc
index bd1bd8fbb9c..ab50c327e28 100644
--- a/storage/innobase/handler/handler0alter.cc
+++ b/storage/innobase/handler/handler0alter.cc
@@ -4278,10 +4278,17 @@ innobase_add_instant_try(
 			case MYSQL_TYPE_MEDIUM_BLOB:
 			case MYSQL_TYPE_BLOB:
 			case MYSQL_TYPE_LONG_BLOB:
+			variable_length:
 				/* Store the empty string for 'core'
 				variable-length NOT NULL columns. */
 				dfield_set_data(d, field_ref_zero, 0);
 				break;
+			case MYSQL_TYPE_STRING:
+				if (col->mbminlen != col->mbmaxlen
+				    || !dict_table_is_comp(user_table)) {
+					goto variable_length;
+				}
+				/* fall through */
 			default:
 				/* For fixed-length NOT NULL 'core' columns,
 				get a dummy default value from SQL. Note that