diff --git a/src/epochs.jl b/src/epochs.jl
index d25d853..181d3f1 100644
--- a/src/epochs.jl
+++ b/src/epochs.jl
@@ -116,6 +116,10 @@ function Base.convert(::Type{Epoch}, dt::TimeType)
     return Epoch(ms_since_unix + EPOCH_OFFSET_MILLISECONDS)
 end
 
+for t in (:Epoch, :Epoch16, :TT2000)
+    @eval Base.convert(::Type{$t}, dt::$t) = dt
+end
+
 for f in (:year, :month, :day, :hour, :minute, :second, :millisecond)
     @eval Dates.$f(epoch::CDFDateTime) = Dates.$f(DateTime(epoch))
 end
diff --git a/test/epochs_test.jl b/test/epochs_test.jl
index 3f525c7..08d8969 100644
--- a/test/epochs_test.jl
+++ b/test/epochs_test.jl
@@ -26,6 +26,8 @@ end
     @test floor(TT2000(0), Minute(1)) == DateTime(2000, 1, 1, 11, 58)
     @test TT2000(0) + Minute(1) == TT2000(60_000_000_000)
 
+    @test TT2000(TT2000(663940869211021568)) == TT2000(663940869211021568)
+
     @test string(TT2000(0)) == "2000-01-01T11:58:55.816"
     @test TT2000(0) == TT2000(0) |> bswap
     @test TT2000(0) == DateTime("2000-01-01T11:58:55.816")