diff --git a/mysql-test/r/gis-rtree.result b/mysql-test/r/gis-rtree.result
index dbd6783fe76..61a96afd8dc 100644
--- a/mysql-test/r/gis-rtree.result
+++ b/mysql-test/r/gis-rtree.result
@@ -862,6 +862,13 @@ CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
 DROP TABLE t1;
+CREATE TABLE t1(foo GEOMETRY NOT NULL, SPATIAL INDEX(foo) );
+INSERT INTO t1(foo) VALUES (NULL);
+ERROR 23000: Column 'foo' cannot be null
+INSERT INTO t1() VALUES ();
+ERROR 22003: Cannot get geometry object from data you send to the GEOMETRY field
+INSERT INTO t1(foo) VALUES ('');
+ERROR 22003: Cannot get geometry object from data you send to the GEOMETRY field
 CREATE TABLE t1 (foo GEOMETRY NOT NULL, SPATIAL INDEX(foo) );
 INSERT INTO t1 (foo) VALUES (PointFromWKB(POINT(1,1)));
 INSERT INTO t1 (foo) VALUES (PointFromWKB(POINT(1,0)));
diff --git a/mysql-test/t/gis-rtree.test b/mysql-test/t/gis-rtree.test
index 09cdcb2435e..e34dd14dbfc 100644
--- a/mysql-test/t/gis-rtree.test
+++ b/mysql-test/t/gis-rtree.test
@@ -242,3 +242,15 @@ INSERT INTO t1 (foo) VALUES (PointFromWKB(POINT(0,0)));
 SELECT 1 FROM t1 WHERE foo != PointFromWKB(POINT(0,0));
 DROP TABLE t1;
 # End of 4.1 tests
+
+#
+# bug #21790 (UNKNOWN ERROR on NULLs in RTree)
+#
+CREATE TABLE t1(foo GEOMETRY NOT NULL, SPATIAL INDEX(foo) );
+--error 1048
+INSERT INTO t1(foo) VALUES (NULL);
+--error 1416
+INSERT INTO t1() VALUES ();
+--error 1416
+INSERT INTO t1(foo) VALUES ('');
+DROP TABLE t1;
diff --git a/sql/handler.cc b/sql/handler.cc
index ccf1a1ef8d9..70c90b01495 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -2115,8 +2115,8 @@ void handler::print_error(int error, myf errflag)
     break;
   }
   case HA_ERR_NULL_IN_SPATIAL:
-    textno= ER_UNKNOWN_ERROR;
-    break;
+    my_error(ER_CANT_CREATE_GEOMETRY_OBJECT, MYF(0));
+    DBUG_VOID_RETURN;
   case HA_ERR_FOUND_DUPP_UNIQUE:
     textno=ER_DUP_UNIQUE;
     break;