diff --git a/src/UnweightedSamplingMulti.jl b/src/UnweightedSamplingMulti.jl
index f1b67c0..3e1d8e0 100644
--- a/src/UnweightedSamplingMulti.jl
+++ b/src/UnweightedSamplingMulti.jl
@@ -7,7 +7,8 @@ function itsample(rng::AbstractRNG, iter, n::Int; alloc = true, iter_type = Any)
     if alloc 
         unweighted_sampling_multi(iter, rng, n)
     else
-        unweighted_resorvoir_sampling_multi(iter, rng, n, iter_type)
+        IterHasKnownSize = Base.IteratorSize(iter)
+        unweighted_resorvoir_sampling_multi(iter, rng, n, IterHasKnownSize, iter_type)
     end
 end
 
@@ -20,7 +21,8 @@ function itsample(rng::AbstractRNG, iter, condition::Function, n::Int; alloc = t
         unweighted_sampling_with_condition_multi(iter, rng, n, condition)
     else
         iter_filtered = Iterators.filter(x -> condition(x), iter)
-        unweighted_resorvoir_sampling_multi(iter_filtered, rng, n, iter_type)
+        IterHasKnownSize = Base.IteratorSize(iter_filtered)
+        unweighted_resorvoir_sampling_multi(iter_filtered, rng, n, IterHasKnownSize, iter_type)
     end
 end
 
@@ -50,7 +52,7 @@ function unweighted_sampling_with_condition_multi(iter, rng, n, condition)
     return res[1:i] 
 end
 
-function unweighted_resorvoir_sampling_multi(iter, rng, n, iter_type = Any)
+function unweighted_resorvoir_sampling_multi(iter, rng, n, ::Base.SizeUnknown, iter_type = eltype(iter))
     it = iterate(iter)
     isnothing(it) && return iter_type[]
     el, state = it
@@ -77,4 +79,19 @@ function unweighted_resorvoir_sampling_multi(iter, rng, n, iter_type = Any)
         reservoir[rand(rng, 1:n)] = el 
         w *= rand(rng)^(1/n)
     end
+end
+
+function unweighted_resorvoir_sampling_multi(iter, rng, n, ::Union{Base.HasLength, Base.HasShape}, iter_type = eltype(iter))
+    N = length(iter)
+    N <= n && return collect(iter)
+    indices = sort!(sample(rng, 1:N, n; replace=false))
+    reservoir = Vector{iter_type}(undef, n)
+    j = 1
+    for (i, x) in enumerate(iter)
+        if i == indices[j]
+            reservoir[j] = x
+            j == n && return reservoir
+            j += 1
+        end
+    end
 end
\ No newline at end of file
diff --git a/src/UnweightedSamplingSingle.jl b/src/UnweightedSamplingSingle.jl
index d7d8483..73caa30 100644
--- a/src/UnweightedSamplingSingle.jl
+++ b/src/UnweightedSamplingSingle.jl
@@ -7,7 +7,8 @@ function itsample(rng::AbstractRNG, iter; alloc = false)
     if alloc 
         unweighted_sampling_single(iter, rng)
     else
-        unweighted_resorvoir_sampling_single(iter, rng)
+        IterHasKnownSize = Base.IteratorSize(iter)
+        unweighted_resorvoir_sampling_single(iter, rng, IterHasKnownSize)
     end
 end
 
@@ -20,11 +21,11 @@ function itsample(rng::AbstractRNG, iter, condition::Function; alloc = false)
         unweighted_sampling_with_condition_single(iter, rng, condition)
     else
         iter_filtered = Iterators.filter(x -> condition(x), iter)
-        unweighted_resorvoir_sampling_single(iter_filtered, rng)
+        IterHasKnownSize = Base.IteratorSize(iter_filtered)
+        unweighted_resorvoir_sampling_single(iter_filtered, rng, IterHasKnownSize)
     end
 end
 
-
 function unweighted_sampling_single(iter, rng)
     pop = collect(iter)
     isempty(pop) && return nothing
@@ -44,7 +45,7 @@ function unweighted_sampling_with_condition_single(iter, rng, condition)
     return nothing
 end
 
-function unweighted_resorvoir_sampling_single(iter, rng)
+function unweighted_resorvoir_sampling_single(iter, rng, ::Base.SizeUnknown)
     res = iterate(iter)
     isnothing(res) && return nothing
     w = rand(rng)
@@ -61,4 +62,13 @@ function unweighted_resorvoir_sampling_single(iter, rng)
         isnothing(res) && return choice
         w *= rand(rng)
     end
-end
\ No newline at end of file
+end
+
+function unweighted_resorvoir_sampling_single(iter, rng, ::Union{Base.HasLength, Base.HasShape})
+    k = rand(rng, 1:length(iter))
+    for (i, x) in enumerate(iter)
+        i == k && return x
+    end
+end
+
+
diff --git a/test/unweighted_sampling_multi_tests.jl b/test/unweighted_sampling_multi_tests.jl
index 2d64409..8d9fce0 100644
--- a/test/unweighted_sampling_multi_tests.jl
+++ b/test/unweighted_sampling_multi_tests.jl
@@ -2,27 +2,44 @@
 @testset "Unweighted sampling multi tests" begin
 	@testset "alloc=$(alloc)" for alloc in [false, true]
 
-		# test values are inrange
 		a, b = 1, 10
-		s = itsample(a:b, 2, alloc=alloc)
+		# test return values of iter with known lengths are inrange
+		iter = a:b
+		s = itsample(iter, 2, alloc=alloc)
 		@test length(s) == 2
 		@test all(x -> a <= x <= b, s)
 
 		@test typeof(s) == Vector{ifelse(alloc, Int, Any)}
-		s = itsample(a:b, 2, alloc=alloc, iter_type=Int)
+		s = itsample(iter, 2, alloc=alloc, iter_type=Int)
 		@test length(s) == 2
 		@test all(x -> a <= x <= b, s)
 		@test typeof(s) == Vector{Int}
-		s = itsample(a:b, 100, alloc=alloc)
+		s = itsample(iter, 100, alloc=alloc)
 		@test length(s) == 10
 		@test length(unique(s)) == 10
 
+		# test return values of iter with unknown lengths are inrange
+		iter = Iterators.filter(x -> x < 5, a:b)
+		s = itsample(iter, 2, alloc=alloc)
+		@test length(s) == 2
+		@test all(x -> a <= x <= b, s)
+
+		@test typeof(s) == Vector{ifelse(alloc, Int, Any)}
+		s = itsample(iter, 2, alloc=alloc, iter_type=Int)
+		@test length(s) == 2
+		@test all(x -> a <= x <= b, s)
+		@test typeof(s) == Vector{Int}
+		s = itsample(iter, 100, alloc=alloc)
+		@test length(s) == 4
+		@test length(unique(s)) == 4
+
 		# create empirical distribution
+		iter = a:b
 		rng = StableRNG(43)
 		reps = 10000
 		dict_res = Dict{Vector, Int}()
 		for _ in 1:reps
-			s = itsample(rng, a:b, 2, alloc=alloc)
+			s = itsample(rng, iter, 2, alloc=alloc)
 			if s in keys(dict_res)
 				dict_res[s] += 1
 			elseif ifelse(alloc, Int, Any)[s[2], s[1]] in keys(dict_res)