diff --git a/gcc/fortran/check.c b/gcc/fortran/check.c
index 625473c90d129646161d5f1bfdc431e80ef9a061..b4db9337e9fe1d075e249c8974c284872c3ef493 100644
--- a/gcc/fortran/check.c
+++ b/gcc/fortran/check.c
@@ -5185,6 +5185,12 @@ is_c_interoperable (gfc_expr *expr, const char **msg, bool c_loc, bool c_f_ptr)
       return false;
     }
 
+  if (expr->ts.type == BT_BOZ)
+    {
+      *msg = "BOZ literal constant";
+      return false;
+    }
+
   if (expr->ts.type == BT_CLASS)
     {
       *msg = "Expression is polymorphic";
diff --git a/gcc/testsuite/gfortran.dg/illegal_boz_arg_3.f90 b/gcc/testsuite/gfortran.dg/illegal_boz_arg_3.f90
new file mode 100644
index 0000000000000000000000000000000000000000..59fefa909714e5e0c752d51344b632143c60e0c8
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/illegal_boz_arg_3.f90
@@ -0,0 +1,7 @@
+! { dg-do compile }
+! PR fortran/103778
+
+program p
+  use iso_c_binding, only : c_sizeof
+  integer, parameter :: a = c_sizeof(z'1') ! { dg-error "cannot appear" }
+end