diff --git a/source/vibe/core/parallelism.d b/source/vibe/core/parallelism.d
index 8a3b2d8..811cce2 100644
--- a/source/vibe/core/parallelism.d
+++ b/source/vibe/core/parallelism.d
@@ -13,6 +13,7 @@ import vibe.core.channel;
 import vibe.core.concurrency : isWeaklyIsolated;
 import vibe.core.log;
 import std.range : ElementType, isInputRange;
+import std.traits : hasMember;
 
 
 /** Processes a range of items in worker tasks and returns them as an unordered
@@ -65,6 +66,9 @@ auto parallelUnorderedMap(alias fun, R)(R items, shared(TaskPool) task_pool, Cha
 			chout.close();
 	}
 
+	static if (hasMember!(R, "length"))
+		auto length = items.length;
+
 	runTask(&senderFun, items, chin);
 
 	auto rc = new shared int;
@@ -77,8 +81,21 @@ auto parallelUnorderedMap(alias fun, R)(R items, shared(TaskPool) task_pool, Cha
 			Channel!O m_channel;
 			O m_front;
 			bool m_gotFront = false;
+			static if (hasMember!(R, "length")) typeof(items.length) m_length;
 		}
 
+		static if (hasMember!(R, "length"))
+			this(Channel!O chout, typeof(items.length) length)
+			{
+				m_channel = chout;
+				m_length = length;
+			}
+		else
+			this(Channel!O chout)
+			{
+				m_channel = chout;
+			}
+
 		@property bool empty()
 		{
 			fetchFront();
@@ -96,8 +113,12 @@ auto parallelUnorderedMap(alias fun, R)(R items, shared(TaskPool) task_pool, Cha
 		{
 			fetchFront();
 			m_gotFront = false;
+			static if (hasMember!(R, "length"))  m_length--;
 		}
 
+		static if (hasMember!(R, "length"))
+			auto length() const { return m_length; }
+
 		private void fetchFront()
 		{
 			if (m_gotFront) return;
@@ -105,7 +126,10 @@ auto parallelUnorderedMap(alias fun, R)(R items, shared(TaskPool) task_pool, Cha
 		}
 	}
 
-	return Result(chout);
+	static if (hasMember!(R, "length"))
+		return Result(chout, length);
+	else
+		return Result(chout);
 }
 
 /// ditto
@@ -128,6 +152,16 @@ unittest {
 	assert(res.isPermutation(iota(100).map!(i => 2 * i).array));
 }
 
+unittest {
+	import std.range : iota;
+
+	auto res = iota(100)
+		.parallelUnorderedMap!(i => 2 * i);
+	assert(res.length == 100);
+	res.popFront();
+	assert(res.length == 99);
+}
+
 
 /** Processes a range of items in worker tasks and returns them as an ordered
 	range.
@@ -159,6 +193,13 @@ auto parallelMap(alias fun, R)(R items, shared(TaskPool) task_pool, ChannelConfi
 		size_t m_index = 0, m_minIndex = -1;
 		Array!SR m_buffer;
 		int m_refCount = 0;
+		static if (hasMember!(R, "length")) typeof(items.length) m_length;
+
+		this(typeof(resunord) source)
+		{
+			m_source = source.move;
+			static if (hasMember!(R, "length")) m_length = m_source.length;
+		}
 
 		@property bool empty()
 		{
@@ -207,6 +248,8 @@ auto parallelMap(alias fun, R)(R items, shared(TaskPool) task_pool, ChannelConfi
 		@property bool empty() { return state.empty; }
 		@property ref O front() { return state.front; }
 		void popFront() { state.popFront; }
+
+		static if (hasMember!(R, "length")) auto length() const { return state.m_length - state.m_index; }
 	}
 
 	return Result(RefCounted!State(resunord.move));
@@ -251,3 +294,15 @@ unittest {
 		.array;
 	assert(res == iota(100).map!(i => 2 * i).array);
 }
+
+unittest {
+	import std.range : iota;
+
+	auto res = iota(100)
+		.parallelMap!(i => 2 * i);
+	assert(res.length == 100);
+	assert(res.front == 0);
+	res.popFront();
+	assert(res.length == 99);
+	assert(res.front == 2);
+}