diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
index 6050359d5210fbe5f0dfd786ee9617099d2e3803..49fb37864bd7a2af563b30af656ee5b92a3a5d62 100644
--- a/gcc/fortran/symbol.cc
+++ b/gcc/fortran/symbol.cc
@@ -5139,6 +5139,10 @@ gfc_type_compatible (gfc_typespec *ts1, gfc_typespec *ts2)
   bool is_union1 = (ts1->type == BT_UNION);
   bool is_union2 = (ts2->type == BT_UNION);
 
+  /* A boz-literal-constant has no type.  */
+  if (ts1->type == BT_BOZ || ts2->type == BT_BOZ)
+    return false;
+
   if (is_class1
       && ts1->u.derived->components
       && ((ts1->u.derived->attr.is_class
diff --git a/gcc/testsuite/gfortran.dg/illegal_boz_arg_4.f90 b/gcc/testsuite/gfortran.dg/illegal_boz_arg_4.f90
new file mode 100644
index 0000000000000000000000000000000000000000..856cfa9211f9c78363503d5173ce481cb6b7d936
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/illegal_boz_arg_4.f90
@@ -0,0 +1,13 @@
+! { dg-do compile }
+! { dg-options "-std=f2018" }
+! PR fortran/103413
+! Contributed by G.Steinmetz
+
+program p
+  type t
+     class(*), allocatable :: a
+  end type
+  type(t) :: x
+  allocate (x%a, source=z'1') ! { dg-error "type incompatible" }
+  allocate (x%a, mold=z'1')   ! { dg-error "type incompatible" }
+end