diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index 1c9b0c5cb622f299a7387aa4cbbfd3399670961b..dd4b26680e04f30324493a40803151b4aa360946 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -11999,6 +11999,7 @@ start:
 	    /* Assigning a class object always is a regular assign.  */
 	    if (code->expr2->ts.type == BT_CLASS
 		&& code->expr1->ts.type == BT_CLASS
+		&& CLASS_DATA (code->expr2)
 		&& !CLASS_DATA (code->expr2)->attr.dimension
 		&& !(gfc_expr_attr (code->expr1).proc_pointer
 		     && code->expr2->expr_type == EXPR_VARIABLE
diff --git a/gcc/testsuite/gfortran.dg/PR10018.f90 b/gcc/testsuite/gfortran.dg/PR10018.f90
new file mode 100644
index 0000000000000000000000000000000000000000..f1cf2676f854a5a180c18954ee6b653cf39c840e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/PR10018.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+!
+subroutine foo(that)
+  implicit none
+  class(*),  target, intent(in)  :: this
+  class(*), pointer, intent(out) :: that
+
+  that => this
+  return
+end subroutine foo
+! { dg-error "Symbol at \\\(1\\\) is not a DUMMY variable" "" { target "*-*-*" } 5 }