Index: driver/options.c
===================================================================
--- driver/options.c	(revision 1012)
+++ driver/options.c	(working copy)
@@ -381,19 +381,31 @@
             if (trans_supported(dbc))
             {
                 char buff[80];
-                const char *level;
+                const char *level= NULL;
 
-                if ((SQLINTEGER)(SQLLEN)ValuePtr & SQL_TXN_SERIALIZABLE)
+                if ((SQLINTEGER)ValuePtr == SQL_TXN_SERIALIZABLE)
                     level="SERIALIZABLE";
-                else if ((SQLINTEGER)(SQLLEN)ValuePtr & SQL_TXN_REPEATABLE_READ)
+                else if ((SQLINTEGER)ValuePtr == SQL_TXN_REPEATABLE_READ)
                     level="REPEATABLE READ";
-                else if ((SQLINTEGER)(SQLLEN)ValuePtr & SQL_TXN_REPEATABLE_READ)
+                else if ((SQLINTEGER)ValuePtr == SQL_TXN_READ_COMMITTED)
                     level="READ COMMITTED";
+                else if ((SQLINTEGER)ValuePtr == SQL_TXN_READ_UNCOMMITTED)
+                    level="READ UNCOMMITTED";
+
+                if (level)
+                {
+                  SQLRETURN rc;
+                  sprintf(buff,"SET SESSION TRANSACTION ISOLATION LEVEL %s",
+                          level);
+                  if (SQL_SUCCEEDED(rc = odbc_stmt(dbc,buff)))
+                      dbc->txn_isolation= (SQLINTEGER)ValuePtr;
+                  return rc;
+                }
                 else
-                    level="READ UNCOMMITTED";
-                sprintf(buff,"SET SESSION TRANSACTION ISOLATION LEVEL %s",level);
-                if (odbc_stmt(dbc,buff) == SQL_SUCCESS)
-                    dbc->txn_isolation= (SQLINTEGER)(SQLLEN)ValuePtr;
+                {
+                  return set_dbc_error(dbc, "HY024",
+                                       "Invalid attribute value", 0);
+                }
             }
             break;
 
Index: test/my_basics.c
===================================================================
--- test/my_basics.c	(revision 1012)
+++ test/my_basics.c	(working copy)
@@ -505,6 +505,54 @@
 }
 
 
+/*
+  Bug #31959 - Allows dirty reading with SQL_TXN_READ_COMMITTED
+               isolation through ODBC
+*/
+DECLARE_TEST(t_bug31959)
+{
+  SQLCHAR level[50] = "uninitialized";
+  SQLINTEGER i;
+  SQLINTEGER levelid[] = {SQL_TXN_SERIALIZABLE, SQL_TXN_REPEATABLE_READ,
+                          SQL_TXN_READ_COMMITTED, SQL_TXN_READ_UNCOMMITTED};
+  SQLCHAR *levelname[] = {"SERIALIZABLE", "REPEATABLE-READ",
+                          "READ-COMMITTED", "READ-UNCOMMITTED"};
+
+  ok_stmt(hstmt, SQLPrepare(hstmt, "select @@tx_isolation", SQL_NTS));
+
+  /* check all 4 valid isolation levels */
+  for(i = 3; i >= 0; --i)
+  {
+    ok_con(hdbc, SQLSetConnectAttr(hdbc, SQL_ATTR_TXN_ISOLATION,
+                                   (SQLPOINTER)levelid[i], 0));
+    ok_stmt(hstmt, SQLExecute(hstmt));
+    ok_stmt(hstmt, SQLFetch(hstmt));
+    ok_stmt(hstmt, SQLGetData(hstmt, 1, SQL_C_CHAR, level, 50, NULL));
+    is_str(level, levelname[i], strlen(levelname[i]));
+    printMessage("Level = %s\n", level);
+    ok_stmt(hstmt, SQLFreeStmt(hstmt, SQL_CLOSE));
+  }
+
+  /* check invalid value (and corresponding SQL state) */
+  is(SQLSetConnectAttr(hdbc, SQL_ATTR_TXN_ISOLATION, (SQLPOINTER)999, 0) ==
+     SQL_ERROR);
+  {
+  SQLCHAR     sql_state[6];
+  SQLINTEGER  err_code= 0;
+  SQLCHAR     err_msg[SQL_MAX_MESSAGE_LENGTH]= {0};
+  SQLSMALLINT err_len= 0;
+
+  memset(err_msg, 'C', SQL_MAX_MESSAGE_LENGTH);
+  SQLGetDiagRec(SQL_HANDLE_DBC, hdbc, 1, sql_state, &err_code, err_msg,
+                SQL_MAX_MESSAGE_LENGTH - 1, &err_len);
+
+  is_str(sql_state, (SQLCHAR *)"HY024", 5);
+  }
+
+  return OK;
+}
+
+
 BEGIN_TESTS
   ADD_TEST(my_basics)
   ADD_TEST(t_max_select)
@@ -520,6 +568,7 @@
   ADD_TEST(t_bug30774)
   ADD_TEST(t_bug30840)
   ADD_TEST(t_bug32727)
+  ADD_TEST(t_bug31959)
 END_TESTS