Error “Column does not belong to referenced table.” in procedure with update clause

I work with IBExpert. I want to increase column STIP by IND percent in update clause in my stored procedure PR_INDEXSTIP. For example, if input parameter will be 0.25, I need to increase my field STIP by 25%. And I think that in set clause I should to write: STIP = 1.25*STIP. So, I have this code (don’t pay attention to returns clause):

CREATE PROCEDURE PR_INDEXSTIP
(IND DECIMAL (8,2))
RETURNS (RESULT INT)
AS 
BEGIN
UPDATE STUDENTS
SET STIP = :STIP*(1+IND);
END

I have an error in this code:

Column does not belong to referenced table.
Dynamic SQL Error.
SQL error code = -206.
Column unknown.
STIP.
At line 7, column 13.
-------------------------------------------
SQLCODE: -206
GDSCODE: 335544569

I can’t resolve this error. I tried to write many different code variations and I still have the error that column STIP is unknown.

Answer

I resolved this problem.

Code:

CREATE PROCEDURE PR_INDEXSTIP
(IND DECIMAL (8,2))
RETURNS (RESULT INT)
AS 
BEGIN
UPDATE STUDENTS
SET STIP = STIP*(1+:IND);
END