diff --git a/session/test/variable/variable_test.go b/session/test/variable/variable_test.go
index 00a5089a28704..0becbd36257b1 100644
--- a/session/test/variable/variable_test.go
+++ b/session/test/variable/variable_test.go
@@ -616,16 +616,28 @@ func TestSessionAlias(t *testing.T) {
 	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows(""))
 	// normal set
 	tk.MustExec("set @@tidb_session_alias='alias123'")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
 	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows("alias123"))
 	// set a long value
 	val := "0123456789012345678901234567890123456789012345678901234567890123456789"
 	tk.MustExec("set @@tidb_session_alias=?", val)
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1292 Truncated incorrect tidb_session_alias value: '0123456789012345678901234567890123456789012345678901234567890123456789'"))
 	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows(val[:64]))
-	// an invalid value
-	err := tk.ExecToErr("set @@tidb_session_alias='abc '")
-	require.EqualError(t, err, "[variable:1231]Incorrect value for variable @@tidb_session_alias 'abc '")
-	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows(val[:64]))
+	// set a long value with unicode
+	val = "中文测试1中文测试2中文测试3中文测试4中文测试5中文测试6中文测试7中文测试8中文测试9中文测试0中文测试a中文测试b中文测试c"
+	tk.MustExec("set @@tidb_session_alias=?", val)
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1292 Truncated incorrect tidb_session_alias value: '中文测试1中文测试2中文测试3中文测试4中文测试5中文测试6中文测试7中文测试8中文测试9中文测试0中文测试a中文测试b中文测试c'"))
+	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows("中文测试1中文测试2中文测试3中文测试4中文测试5中文测试6中文测试7中文测试8中文测试9中文测试0中文测试a中文测试b中文测试"))
+	// end with space
+	tk.MustExec("set @@tidb_session_alias='abc  '")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1292 Truncated incorrect tidb_session_alias value: 'abc  '"))
+	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows("abc"))
+	// end with space after truncate
+	tk.MustExec("set @@tidb_session_alias='abc                                                                    1'")
+	tk.MustQuery("show warnings").Check(testkit.Rows("Warning 1292 Truncated incorrect tidb_session_alias value: 'abc                                                                    1'"))
+	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows("abc"))
 	// reset to empty
 	tk.MustExec("set @@tidb_session_alias=''")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
 	tk.MustQuery("select @@tidb_session_alias").Check(testkit.Rows(""))
 }
diff --git a/sessionctx/variable/sysvar.go b/sessionctx/variable/sysvar.go
index bf358da6f53fd..3226d6242d587 100644
--- a/sessionctx/variable/sysvar.go
+++ b/sessionctx/variable/sysvar.go
@@ -2817,13 +2817,23 @@ var defaultSysVars = []*SysVar{
 	}},
 	{Scope: ScopeSession, Name: TiDBSessionAlias, Value: "", Type: TypeStr,
 		Validation: func(s *SessionVars, normalizedValue string, originalValue string, _ ScopeFlag) (string, error) {
-			if len(normalizedValue) > 64 {
+			chars := []rune(normalizedValue)
+			warningAdded := false
+			if len(chars) > 64 {
 				s.StmtCtx.AppendWarning(ErrTruncatedWrongValue.GenWithStackByArgs(TiDBSessionAlias, originalValue))
-				normalizedValue = normalizedValue[:64]
+				warningAdded = true
+				chars = chars[:64]
+				normalizedValue = string(chars)
 			}
 
-			if len(normalizedValue) > 0 && util.IsInCorrectIdentifierName(normalizedValue) {
-				return "", ErrWrongValueForVar.GenWithStack("Incorrect value for variable @@%s '%s'", TiDBSessionAlias, normalizedValue)
+			// truncate to a valid identifier
+			for normalizedValue != "" && util.IsInCorrectIdentifierName(normalizedValue) {
+				if !warningAdded {
+					s.StmtCtx.AppendWarning(ErrTruncatedWrongValue.GenWithStackByArgs(TiDBSessionAlias, originalValue))
+					warningAdded = true
+				}
+				chars = chars[:len(chars)-1]
+				normalizedValue = string(chars)
 			}
 
 			return normalizedValue, nil