diff --git a/base/deepcopy.jl b/base/deepcopy.jl
index 01c0d3bbd61e5..45a7755a77ae6 100644
--- a/base/deepcopy.jl
+++ b/base/deepcopy.jl
@@ -96,7 +96,7 @@ function _deepcopy_array_t(@nospecialize(x), T, stackdict::IdDict)
     return dest
 end
 
-function deepcopy_internal(x::Dict, stackdict::IdDict)
+function deepcopy_internal(x::Union{Dict,IdDict}, stackdict::IdDict)
     if haskey(stackdict, x)
         return stackdict[x]::typeof(x)
     end
diff --git a/test/copy.jl b/test/copy.jl
index 80052a1cc6465..fd0128c2a661a 100644
--- a/test/copy.jl
+++ b/test/copy.jl
@@ -153,4 +153,14 @@ end
         @test bar2.foo ∈ keys(bar2.fooDict)
         @test bar2.fooDict[bar2.foo] != nothing
     end
+
+    let d = IdDict(rand(2) => rand(2) for i = 1:100)
+        d2 = deepcopy(d)
+        for k in keys(d2)
+            @test haskey(d2, k)
+        end
+        for k in keys(d)
+            @test haskey(d, k)
+        end
+    end
 end