Index: modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.254
diff -u -p -r1.254 system.install
--- modules/system/system.install	15 May 2008 20:55:58 -0000	1.254
+++ modules/system/system.install	8 Jun 2008 15:02:00 -0000
@@ -305,9 +305,15 @@ function system_requirements($phase) {
 function system_install() {
   if ($GLOBALS['db_type'] == 'pgsql') {
     // Create unsigned types.
-    db_query("CREATE DOMAIN int_unsigned integer CHECK (VALUE >= 0)");
-    db_query("CREATE DOMAIN smallint_unsigned smallint CHECK (VALUE >= 0)");
-    db_query("CREATE DOMAIN bigint_unsigned bigint CHECK (VALUE >= 0)");
+    if (!db_result(db_query("SELECT COUNT(*) FROM pg_constraint WHERE conname = 'int_unsigned_check'"))) {
+      db_query("CREATE DOMAIN int_unsigned integer CHECK (VALUE >= 0)");
+    }
+    if (!db_result(db_query("SELECT COUNT(*) FROM pg_constraint WHERE conname = 'smallint_unsigned_check'"))) {
+      db_query("CREATE DOMAIN smallint_unsigned smallint CHECK (VALUE >= 0)");
+    }
+    if (!db_result(db_query("SELECT COUNT(*) FROM pg_constraint WHERE conname = 'bigint_unsigned_check'"))) {
+      db_query("CREATE DOMAIN bigint_unsigned bigint CHECK (VALUE >= 0)");
+    }
 
     // Create functions.
     db_query('CREATE OR REPLACE FUNCTION "greatest"(numeric, numeric) RETURNS numeric AS