diff --git a/testsuite/tests/concurrent/prog001/all.T b/testsuite/tests/concurrent/prog001/all.T
index e3195833a0307510a279ec3badb9114a7bf6376c..39327b0a850c94f8aa6e1c9f28a7df280f96a383 100644
--- a/testsuite/tests/concurrent/prog001/all.T
+++ b/testsuite/tests/concurrent/prog001/all.T
@@ -14,5 +14,6 @@
 
 test('concprog001', [extra_files(['Arithmetic.hs', 'Converter.hs', 'Mult.hs', 'Stream.hs', 'Thread.hs', 'Trit.hs', 'Utilities.hs']),
                      when(fast(), skip), only_ways(['threaded2']),
+                     fragile(16604),
                      run_timeout_multiplier(2)],
      multimod_compile_and_run, ['Mult', ''])