Abstract We consider the problem of existence and uniqueness of extensions for the solutions of the Pexider type equation f ( x + y ) = g ( x ) + h ( y ) + k ( x ) l ( y ) {f(x+y)=g(x)+h(y)+k(x)l(y)} for ( x , y ) ∈ D {(x,y)\in D} , where X is a normed space and D is a nonempty open and connected subset of X 2 {X^{2}} .