diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index e1af050..1ea6292 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -13,6 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         version:
+          - '1.0'    # 1.0 is only partially tested; in the next breaking release, add [compat] 'julia = "1.6"' and drop this
           - '1.6'
           - '1'
           - 'nightly'
diff --git a/Project.toml b/Project.toml
index 45c875d..04ad672 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,9 +1,7 @@
 name = "AbstractTrees"
 uuid = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"
-version = "0.4.1"
 authors = ["Keno Fischer <keno@alumni.harvard.edu>"]
-
-[deps]
+version = "0.4.2"
 
 [compat]
 julia = "1"
diff --git a/src/AbstractTrees.jl b/src/AbstractTrees.jl
index 561915b..10f8773 100644
--- a/src/AbstractTrees.jl
+++ b/src/AbstractTrees.jl
@@ -19,6 +19,11 @@ include("iteration.jl")
 include("builtins.jl")
 include("printing.jl")
 
+# Julia 1.0 support (delete when we no longer support it)
+if !isdefined(Base, :isnothing)
+    isnothing(x) = x === nothing
+end
+
 
 #interface
 export ParentLinks, StoredParents, ImplicitParents
diff --git a/src/base.jl b/src/base.jl
index 9a187ca..3737eec 100644
--- a/src/base.jl
+++ b/src/base.jl
@@ -130,7 +130,7 @@ function is not available.
 Equivalence is established with the `equiv` function.  Note that new methods should also define `equiv` or calls
 may fall back to the default method.
 """
-isdescendant(node1, node2; equiv=(≡)) = !equiv(node1, node2) && intree(node1, node2; equiv)
+isdescendant(node1, node2; equiv=(≡)) = !equiv(node1, node2) && intree(node1, node2; equiv=equiv)
 
 
 """
diff --git a/src/printing.jl b/src/printing.jl
index f696659..3ee4546 100644
--- a/src/printing.jl
+++ b/src/printing.jl
@@ -259,8 +259,8 @@ function print_tree(printnode::Function, io::IO, node;
         end
 
         print_tree(printnode, io, child;
-                   maxdepth, indicate_truncation, charset, printkeys,
-                   depth=depth+1, prefix=child_prefix
+                   maxdepth=maxdepth, indicate_truncation=indicate_truncation, charset=charset,
+                   printkeys=printkeys, depth=depth+1, prefix=child_prefix
                   )
     end
 end
diff --git a/test/examples.jl b/test/examples.jl
index f47c1e4..8d5dd5a 100644
--- a/test/examples.jl
+++ b/test/examples.jl
@@ -1,4 +1,5 @@
 # Ensure that we can run all files in the examples directory with no errors.
+# Note: fstree doesn't work on Julia 1.0
 
 exampledir = joinpath(dirname(@__DIR__), "examples")
 examples = readdir(exampledir)
diff --git a/test/examples/binarytree.jl b/test/examples/binarytree.jl
index 8b85db6..765bd60 100644
--- a/test/examples/binarytree.jl
+++ b/test/examples/binarytree.jl
@@ -1,5 +1,8 @@
 using AbstractTrees
 
+if !isdefined(Base, :isnothing)        # Julia 1.0 support
+    using AbstractTrees: isnothing
+end
 
 mutable struct BinaryNode{T}
     data::T
diff --git a/test/examples/fstree.jl b/test/examples/fstree.jl
index 1453c1c..ca8a501 100644
--- a/test/examples/fstree.jl
+++ b/test/examples/fstree.jl
@@ -29,7 +29,8 @@ AbstractTrees.printnode(io::IO, d::Directory) = print(io, basename(d.path))
 AbstractTrees.printnode(io::IO, f::File) = print(io, basename(f.path))
 
 function mk_tree_test_dir(f, parentdir=tempdir(); prefix="jl_")
-    mktempdir(parentdir; prefix) do path
+    # While Julia 1.0 can parse this, `mktempdir` does not support the `prefix` kw
+    mktempdir(parentdir; prefix=prefix) do path
         cd(path) do
             open(io -> write(io, "test1"), "f1"; write=true)
             mkdir("A")
diff --git a/test/runtests.jl b/test/runtests.jl
index 62a493a..21a7f72 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -3,5 +3,7 @@ using AbstractTrees, Test
 
 @testset "Builtins" begin include("builtins.jl") end
 @testset "Custom tree types" begin include("trees.jl") end
-@testset "Printing" begin include("printing.jl") end
-
+if Base.VERSION >= v"1.6"
+    # Printing tests use `findall` variants that are not supported on Julia 1.0
+    @testset "Printing" begin include("printing.jl") end
+end
diff --git a/test/trees.jl b/test/trees.jl
index 70bf459..c3f80ba 100644
--- a/test/trees.jl
+++ b/test/trees.jl
@@ -88,7 +88,7 @@ end
 include(joinpath(@__DIR__,"examples","fstree.jl"))
 
 @testset "FSNode" begin
-    mk_tree_test_dir() do path
+    Base.VERSION >= v"1.6" && mk_tree_test_dir() do path
         tree = Directory(".")
 
         ls = nodevalue.((collect ∘ Leaves)(tree))