diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 05d7f97f28..c8f74733b0 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -2154,6 +2154,9 @@ function dbDelta( $queries = '', $execute = true ) {
 	 */
 	$iqueries = apply_filters( 'dbdelta_insert_queries', $iqueries );
 
+	$text_fields = array( 'tinytext', 'text', 'mediumtext', 'longtext' );
+	$blob_fields = array( 'tinyblob', 'blob', 'mediumblob', 'longblob' );
+
 	$global_tables = $wpdb->tables( 'global' );
 	foreach ( $cqueries as $table => $qry ) {
 		// Upgrade global tables only for the main site. Don't upgrade at all if conditions are not optimal.
@@ -2223,9 +2226,24 @@ function dbDelta( $queries = '', $execute = true ) {
 
 				// Is actual field type different from the field type in query?
 				if ($tablefield->Type != $fieldtype) {
+					$do_change = true;
+					if ( in_array( strtolower( $fieldtype ), $text_fields ) && in_array( strtolower( $tablefield->Type ), $text_fields ) ) {
+						if ( array_search( strtolower( $fieldtype ), $text_fields ) < array_search( strtolower( $tablefield->Type ), $text_fields ) ) {
+							$do_change = false;
+						}
+					}
+
+					if ( in_array( strtolower( $fieldtype ), $blob_fields ) && in_array( strtolower( $tablefield->Type ), $blob_fields ) ) {
+						if ( array_search( strtolower( $fieldtype ), $blob_fields ) < array_search( strtolower( $tablefield->Type ), $blob_fields ) ) {
+							$do_change = false;
+						}
+					}
+
+					if ( $do_change ) {
 					// Add a query to change the column type
-					$cqueries[] = "ALTER TABLE {$table} CHANGE COLUMN {$tablefield->Field} " . $cfields[strtolower($tablefield->Field)];
-					$for_update[$table.'.'.$tablefield->Field] = "Changed type of {$table}.{$tablefield->Field} from {$tablefield->Type} to {$fieldtype}";
+						$cqueries[] = "ALTER TABLE {$table} CHANGE COLUMN {$tablefield->Field} " . $cfields[strtolower($tablefield->Field)];
+						$for_update[$table.'.'.$tablefield->Field] = "Changed type of {$table}.{$tablefield->Field} from {$tablefield->Type} to {$fieldtype}";
+					}
 				}
 
 				// Get the default value from the array
diff --git a/tests/phpunit/tests/dbdelta.php b/tests/phpunit/tests/dbdelta.php
index a2d2a8586f..d6dc20ac72 100644
--- a/tests/phpunit/tests/dbdelta.php
+++ b/tests/phpunit/tests/dbdelta.php
@@ -31,6 +31,8 @@ class Tests_dbDelta extends WP_UnitTestCase {
 			CREATE TABLE {$wpdb->prefix}dbdelta_test (
 				id bigint(20) NOT NULL AUTO_INCREMENT,
 				column_1 varchar(255) NOT NULL,
+				column_2 text,
+				column_3 blob,
 				PRIMARY KEY  (id),
 				KEY key_1 (column_1),
 				KEY compound_key (id,column_1),
@@ -362,4 +364,104 @@ class Tests_dbDelta extends WP_UnitTestCase {
 
 		$this->assertSame( array(), $actual );
 	}
+
+	/**
+	 * @ticket 36748
+	 */
+	function test_dont_downsize_text_fields() {
+		global $wpdb;
+
+		$result = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				column_2 tinytext,
+				column_3 blob,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compound_key (id,column_1),
+				FULLTEXT KEY fulltext_key (column_1)
+			) ENGINE=MyISAM
+			", false );
+
+		$this->assertSame( array(), $result );
+	}
+
+	/**
+	 * @ticket 36748
+	 */
+	function test_dont_downsize_blob_fields() {
+		global $wpdb;
+
+		$result = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				column_2 text,
+				column_3 tinyblob,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compound_key (id,column_1),
+				FULLTEXT KEY fulltext_key (column_1)
+			) ENGINE=MyISAM
+			", false );
+
+		$this->assertSame( array(), $result );
+	}
+
+	/**
+	 * @ticket 36748
+	 */
+	function test_upsize_text_fields() {
+		global $wpdb;
+
+		$result = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				column_2 bigtext,
+				column_3 blob,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compound_key (id,column_1),
+				FULLTEXT KEY fulltext_key (column_1)
+			) ENGINE=MyISAM
+			", false );
+
+		$this->assertSame(
+			array(
+				"{$wpdb->prefix}dbdelta_test.column_2"
+					=> "Changed type of {$wpdb->prefix}dbdelta_test.column_2 from text to bigtext"
+			), $result );
+	}
+
+	/**
+	 * @ticket 36748
+	 */
+	function test_upsize_blob_fields() {
+		global $wpdb;
+
+		$result = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				column_2 text,
+				column_3 mediumblob,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compound_key (id,column_1),
+				FULLTEXT KEY fulltext_key (column_1)
+			) ENGINE=MyISAM
+			", false );
+
+		$this->assertSame(
+			array(
+				"{$wpdb->prefix}dbdelta_test.column_3"
+					=> "Changed type of {$wpdb->prefix}dbdelta_test.column_3 from blob to mediumblob"
+			), $result );
+	}
 }