diff --git a/src/sage/symbolic/expression.pxd b/src/sage/symbolic/expression.pxd
index be27fb8b224..1fa578d43c3 100644
--- a/src/sage/symbolic/expression.pxd
+++ b/src/sage/symbolic/expression.pxd
@@ -1,4 +1,4 @@
-cpdef bint isinstance(x, Expression)
+cpdef bint is_Expression(x)
 cpdef _repr_Expression(x)
 cpdef _latex_Expression(x)
 cpdef new_Expression(parent, x)