diff --git a/tablex.lua b/tablex.lua
index 38de632..ebaa399 100644
--- a/tablex.lua
+++ b/tablex.lua
@@ -329,41 +329,40 @@ if not tablex.clear then
 end
 
 -- Copy a table
---	See shallow_overlay to shallow copy into another table to avoid garbage.
+--	See shallow_overlay to shallow copy into an existing table to avoid garbage.
 function tablex.shallow_copy(t)
-	assert:type(t, "table", "tablex.copy - t", 1)
-	local into = {}
-	for k, v in pairs(t) do
-		into[k] = v
+	if type(t) == "table" then
+		local into = {}
+		for k, v in pairs(t) do
+			into[k] = v
+		end
+		return into
 	end
-	return into
+	return t
 end
 
 local function deep_copy(t, copied)
-	-- TODO: consider supporting deep_copy(3) so you can always use deep_copy without type checking
-	local into = {}
-	for k, v in pairs(t) do
-		local clone = v
-		if type(v) == "table" then
-			if copied[v] then
-				clone = copied[v]
-			elseif type(v.copy) == "function" then
-				clone = v:copy()
-				assert:type(clone, "table", "copy() didn't return a copy")
-			else
-				clone = deep_copy(v, copied)
-				setmetatable(clone, getmetatable(v))
+	local clone = t
+	if type(t) == "table" then
+		if copied[t] then
+			clone = copied[t]
+		elseif type(t.copy) == "function" then
+			clone = t:copy()
+			assert:type(clone, "table", "copy() didn't return a copy")
+		else
+			clone = {}
+			for k, v in pairs(t) do
+				clone[k] = deep_copy(v, copied)
 			end
-			copied[v] = clone
+			setmetatable(clone, getmetatable(t))
+			copied[t] = clone
 		end
-		into[k] = clone
 	end
-	return into
+	return clone
 end
 -- Recursively copy values of a table.
 -- Retains the same keys as original table -- they're not cloned.
 function tablex.deep_copy(t)
-	assert:type(t, "table", "tablex.deep_copy - t", 1)
 	return deep_copy(t, {})
 end
 
diff --git a/tests.lua b/tests.lua
index 109deb4..57bcdb4 100644
--- a/tests.lua
+++ b/tests.lua
@@ -20,6 +20,10 @@ local function test_shallow_copy()
 	x = { a = { b = { 2 }, c = { 3 }, } }
 	r = tablex.shallow_copy(x)
 	assert:equal(r.a, x.a)
+
+	x = 10
+	r = tablex.shallow_copy(x)
+	assert:equal(r, x)
 end
 
 local function test_deep_copy()
@@ -35,6 +39,10 @@ local function test_deep_copy()
 	assert(r.a ~= x.a)
 	assert:equal(r.a.b[1], 2)
 	assert:equal(r.a.c[1], 3)
+
+	x = 10
+	r = tablex.deep_copy(x)
+	assert:equal(r, x)
 end