diff --git a/sqlbase7_sa/sqlbase7_sa05.py b/sqlbase7_sa/sqlbase7_sa05.py
index 642ada1..2b98c83 100644
--- a/sqlbase7_sa/sqlbase7_sa05.py
+++ b/sqlbase7_sa/sqlbase7_sa05.py
@@ -61,6 +61,9 @@ class SQLBase7Dialect_SA05(SQLBase7Dialect):
         cursor.close()
 
         cursor = connection.connection.cursor()
-        for row in cursor.execute("SELECT COLNAME FROM %s.SYSPKCONSTRAINTS WHERE NAME = '%s' ORDER BY PKCOLSEQNUM" % (table.schema, table.name)):
-            table.append_constraint(PrimaryKeyConstraint(row.COLNAME))
+        key_columns = [row.COLNAME for row in cursor.execute(
+                "SELECT COLNAME FROM %s.SYSPKCONSTRAINTS WHERE NAME = '%s' ORDER BY PKCOLSEQNUM" % (table.schema, table.name)
+                )]
+        if key_columns:
+            table.append_constraint(PrimaryKeyConstraint(*key_columns))
         cursor.close()