diff --git a/mysql-test/r/gis.result b/mysql-test/r/gis.result
index bfd0ddccb90..0dc10c56bd0 100644
--- a/mysql-test/r/gis.result
+++ b/mysql-test/r/gis.result
@@ -1076,4 +1076,19 @@ SPATIAL INDEX i1 (col1, col2)
 );
 ERROR HY000: Incorrect arguments to SPATIAL INDEX
 DROP TABLE t0, t1, t2;
+#
+# Bug#11908153: CRASH AND/OR VALGRIND ERRORS IN FIELD_BLOB::GET_KEY_IMAGE
+#
+CREATE TABLE g1
+(a geometry NOT NULL, UNIQUE KEY i (a(151))) engine=myisam;
+INSERT INTO g1 VALUES (geomfromtext('point(1 1)'));
+INSERT INTO g1 VALUES (geomfromtext('point(1 2)'));
+FLUSH TABLES;
+SELECT 1 FROM g1 
+FORCE INDEX(i) WHERE a = date_sub(now(), interval 2808.4 year_month)
+;
+1
+Warnings:
+Warning	1441	Datetime function: datetime field overflow
+DROP TABLE g1;
 End of 5.5 tests
diff --git a/mysql-test/t/gis.test b/mysql-test/t/gis.test
index 2a800140d1f..104afddeee5 100644
--- a/mysql-test/t/gis.test
+++ b/mysql-test/t/gis.test
@@ -820,5 +820,23 @@ CREATE TABLE t3 (
 # cleanup
 DROP TABLE t0, t1, t2;
 
+--echo #
+--echo # Bug#11908153: CRASH AND/OR VALGRIND ERRORS IN FIELD_BLOB::GET_KEY_IMAGE
+--echo #
+
+CREATE TABLE g1
+(a geometry NOT NULL, UNIQUE KEY i (a(151))) engine=myisam;
+
+INSERT INTO g1 VALUES (geomfromtext('point(1 1)'));
+INSERT INTO g1 VALUES (geomfromtext('point(1 2)'));
+
+FLUSH TABLES;
+
+SELECT 1 FROM g1 
+FORCE INDEX(i) WHERE a = date_sub(now(), interval 2808.4 year_month)
+;
+
+DROP TABLE g1;
+
 
 --echo End of 5.5 tests
diff --git a/sql/field.h b/sql/field.h
index 304e75494e2..9c2cd52cfa5 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -1906,7 +1906,13 @@ public:
   int  store(longlong nr, bool unsigned_val);
   int  store_decimal(const my_decimal *);
   uint size_of() const { return sizeof(*this); }
-  int  reset(void) { return !maybe_null() || Field_blob::reset(); }
+
+  /**
+    Non-nullable GEOMETRY types cannot have defaults,
+    but the underlying blob must still be reset.
+   */
+  int reset(void) { return Field_blob::reset() || !maybe_null(); }
+
   geometry_type get_geometry_type() { return geom_type; };
 };
 #endif /*HAVE_SPATIAL*/
diff --git a/sql/field_conv.cc b/sql/field_conv.cc
index 3890fe395d7..1a3ac9de08b 100644
--- a/sql/field_conv.cc
+++ b/sql/field_conv.cc
@@ -178,7 +178,10 @@ set_field_to_null_with_conversions(Field *field, bool no_conversions)
     ((Field_timestamp*) field)->set_time();
     return 0;					// Ok to set time to NULL
   }
+  
+  // Note: we ignore any potential failure of reset() here.
   field->reset();
+
   if (field == field->table->next_number_field)
   {
     field->table->auto_increment_field_not_null= FALSE;