diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index c300e240f2..9d125d008d 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -1252,6 +1252,7 @@ class wpdb {
 		$query = str_replace( '"%s"', '%s', $query ); // doublequote unquoting
 		$query = preg_replace( '|(?<!%)%f|' , '%F', $query ); // Force floats to be locale unaware
 		$query = preg_replace( '|(?<!%)%s|', "'%s'", $query ); // quote the strings, avoiding escaped strings like %%s
+		$query = preg_replace( '/%(?:%|$|([^dsF]))/', '%%\\1', $query ); // escape any unescaped percents 
 		array_walk( $args, array( $this, 'escape_by_ref' ) );
 		return @vsprintf( $query, $args );
 	}
@@ -2821,7 +2822,8 @@ class wpdb {
 					}
 
 					if ( is_array( $value['length'] ) ) {
-						$queries[ $col ] = $this->prepare( "CONVERT( LEFT( CONVERT( %s USING $charset ), %.0f ) USING $connection_charset )", $value['value'], $value['length']['length'] );
+						$length = sprintf( '%.0f', $value['length']['length'] );
+						$queries[ $col ] = $this->prepare( "CONVERT( LEFT( CONVERT( %s USING $charset ), $length ) USING $connection_charset )", $value['value'] );
 					} else if ( 'binary' !== $charset ) {
 						// If we don't have a length, there's no need to convert binary - it will always return the same result.
 						$queries[ $col ] = $this->prepare( "CONVERT( CONVERT( %s USING $charset ) USING $connection_charset )", $value['value'] );
diff --git a/tests/phpunit/tests/db.php b/tests/phpunit/tests/db.php
index fef24cbcd2..a2626a8236 100644
--- a/tests/phpunit/tests/db.php
+++ b/tests/phpunit/tests/db.php
@@ -273,6 +273,7 @@ class Tests_DB extends WP_UnitTestCase {
 		$this->assertEquals( "UPDATE test_table SET string_column = '%f is a float, %d is an int 3, %s is a string', field = '4'", $sql );
 	}
 
+
 	/**
 	 * Test that SQL modes are set correctly
 	 * @ticket 26847
@@ -1115,4 +1116,14 @@ class Tests_DB extends WP_UnitTestCase {
 		$this->assertSame( 'utf8', $result['charset'] );
 		$this->assertSame( 'utf8_general_ci', $result['collate'] );
 	}
+
+	/**
+	 *
+	 */
+	function test_prepare_with_unescaped_percents() {
+		global $wpdb;
+
+		$sql = $wpdb->prepare( '%d %1$d %%% %', 1 );
+		$this->assertEquals( '1 %1$d %% %', $sql );
+	}
 }