diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c
index 388aca7c38c..c27b47aa98f 100644
--- a/gcc/fortran/simplify.c
+++ b/gcc/fortran/simplify.c
@@ -8123,8 +8123,8 @@ gfc_simplify_transpose (gfc_expr *matrix)
 			       &matrix->where);
   result->rank = 2;
   result->shape = gfc_get_shape (result->rank);
-  mpz_set (result->shape[0], matrix->shape[1]);
-  mpz_set (result->shape[1], matrix->shape[0]);
+  mpz_init_set (result->shape[0], matrix->shape[1]);
+  mpz_init_set (result->shape[1], matrix->shape[0]);

   if (matrix->ts.type == BT_CHARACTER)
     result->ts.u.cl = matrix->ts.u.cl;
diff --git a/gcc/testsuite/gfortran.dg/transpose_5.f90 b/gcc/testsuite/gfortran.dg/transpose_5.f90
new file mode 100644
index 00000000000..682b1c8552b
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/transpose_5.f90
@@ -0,0 +1,8 @@
+! { dg-do compiler }
+! { dg-options "-O2" }
+! PR fortran/99840 - ICE in gfc_simplify_matmul, at fortran/simplify.c:4777
+program p
+  integer, parameter :: x(0,0) = 0
+  integer :: y(0,0)
+  y = matmul (x, transpose(x))
+end