Index: wp-includes/capabilities.php
--- wp-includes/capabilities.php
+++ wp-includes/capabilities.php
@@ -961,8 +961,10 @@
 	case 'delete_post':
 	case 'delete_page':
 		$author_data = get_userdata( $user_id );
-		$post = get_post( $args[0] );
 
+		if ( ! $post = get_post( $args[0] ) )
+			break;
+
 		if ( 'revision' == $post->post_type ) {
 			$post = get_post( $post->post_parent );
 		}
@@ -1011,8 +1013,10 @@
 	case 'edit_post':
 	case 'edit_page':
 		$author_data = get_userdata( $user_id );
-		$post = get_post( $args[0] );
 
+		if ( ! $post = get_post( $args[0] ) )
+			break;
+
 		if ( 'revision' == $post->post_type ) {
 			$post = get_post( $post->post_parent );
 		}
@@ -1060,8 +1064,10 @@
 	case 'read_post':
 	case 'read_page':
 		$author_data = get_userdata( $user_id );
-		$post = get_post( $args[0] );
 
+		if ( ! $post = get_post( $args[0] ) )
+			break;
+
 		if ( 'revision' == $post->post_type ) {
 			$post = get_post( $post->post_parent );
 		}
@@ -1099,7 +1105,10 @@
 	case 'edit_post_meta':
 	case 'delete_post_meta':
 	case 'add_post_meta':
-		$post = get_post( $args[0] );
+
+		if ( ! $post = get_post( $args[0] ) )
+			break;
+
 		$post_type_object = get_post_type_object( $post->post_type );
 		$caps = map_meta_cap( $post_type_object->cap->edit_post, $user_id, $post->ID );
 
@@ -1115,7 +1124,10 @@
 		break;
 	case 'edit_comment':
 		$comment = get_comment( $args[0] );
-		$post = get_post( $comment->comment_post_ID );
+
+		if ( ! $post = get_post( $comment->comment_post_ID ) )
+			break;
+
 		$post_type_object = get_post_type_object( $post->post_type );
 
 		$caps = map_meta_cap( $post_type_object->cap->edit_post, $user_id, $post->ID );