Let
D
(
R
)
\mathcal {D}\left ( {\mathbf {R}} \right )
denote the Schwartz space of all
C
∞
{C^\infty }
-functions
f
:
R
→
C
f:{\mathbf {R}} \to {\mathbf {C}}
with compact supports in the real line
R
{\mathbf {R}}
. An earlier result of the author on the automatic continuity of translation-invariant linear functionals on
D
(
R
)
\mathcal {D}\left ( {\mathbf {R}} \right )
is combined with a general version of the Closed-Graph Theorem due to A. P. Robertson and W. J. Robertson in order to prove that every linear mapping
S
S
of
D
(
R
)
\mathcal {D}\left ( {\mathbf {R}} \right )
into itself, which commutes with translations, is automatically continuous.