colordiff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
new file mode 100644
index 1f6e02d..60a5099
*** a/src/backend/commands/dbcommands.c
--- b/src/backend/commands/dbcommands.c
*************** createdb(const CreatedbStmt *stmt)
*** 549,556 ****
  		/*
  		 * Iterate through all tablespaces of the template database, and copy
  		 * each one to the new database.
  		 */
! 		rel = heap_open(TableSpaceRelationId, AccessShareLock);
  		scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
  		while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
  		{
--- 549,563 ----
  		/*
  		 * Iterate through all tablespaces of the template database, and copy
  		 * each one to the new database.
+ 		 *
+ 		 * We need to use ShareLock to prevent other processes from updating a
+ 		 * tablespace (such as changing an ACL, for example) or we will end up
+ 		 * running into the same tablespace multiple times during our heap scan
+ 		 * (the prior-to-update tuple and then the new tuple after the update)
+ 		 * and copydir() will, rightfully, complain that the directory already
+ 		 * exists.
  		 */
! 		rel = heap_open(TableSpaceRelationId, ShareLock);
  		scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
  		while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
  		{
*************** createdb(const CreatedbStmt *stmt)
*** 607,613 ****
  			}
  		}
  		heap_endscan(scan);
! 		heap_close(rel, AccessShareLock);
  
  		/*
  		 * We force a checkpoint before committing.  This effectively means
--- 614,620 ----
  			}
  		}
  		heap_endscan(scan);
! 		heap_close(rel, ShareLock);
  
  		/*
  		 * We force a checkpoint before committing.  This effectively means