diff --git a/lib/std/collections/list.c3 b/lib/std/collections/list.c3
index 1162df7cd..060974206 100644
--- a/lib/std/collections/list.c3
+++ b/lib/std/collections/list.c3
@@ -79,7 +79,7 @@ fn void List.append(&self, Type element)
 
 /**
  * @require self.size > 0
- */
+ **/
 fn Type List.pop(&self)
 {
 	return self.entries[--self.size];
@@ -92,7 +92,7 @@ fn void List.clear(&self)
 
 /**
  * @require self.size > 0
- */
+ **/
 fn Type List.pop_first(&self)
 {
 	Type value = self.entries[0];
@@ -100,6 +100,9 @@ fn Type List.pop_first(&self)
 	return value;
 }
 
+/**
+ * @require index < self.size
+ **/
 fn void List.remove_at(&self, usz index)
 {
 	for (usz i = index + 1; i < self.size; i++)
@@ -162,6 +165,9 @@ fn void List.push_front(&self, Type type) @inline
 	self.insert_at(0, type);
 }
 
+/**
+ * @require index < self.size
+ **/
 fn void List.insert_at(&self, usz index, Type type)
 {
 	self.ensure_capacity();
@@ -181,11 +187,17 @@ fn void List.set_at(&self, usz index, Type type)
 	self.entries[index] = type;
 }
 
+/**
+ * @require self.size > 0
+ **/
 fn void List.remove_last(&self)
 {
 	self.size--;
 }
 
+/**
+ * @require self.size > 0
+ **/
 fn void List.remove_first(&self)
 {
 	self.remove_at(0);
@@ -235,16 +247,26 @@ fn void List.swap(&self, usz i, usz j)
  * @return "the number of deleted elements"
  **/
 fn usz List.remove_if(&self, ElementPredicate filter)
+{
+	return self._remove_if({ filter }, &Filter.same);
+}
+
+macro usz List._remove_if(&self, Filter o, m) @private
 {
 	usz size = self.size;
-	for (usz i = size; i > 0; i--)
+	usz i = size;
+	usz k = i;
+	while (k > 0)
 	{
-		if (filter(&self.entries[i - 1])) continue;
-		for (usz j = i; j < size; j++)
-		{
-			self.entries[j - 1] = self.entries[j];
-		}
-		self.size--;
+		// Find last index of item to be deleted.
+		while (i > 0 && m(o, &self.entries[i - 1])) i--;
+		// Remove the items from this index up to the one not to be deleted.
+		usz n = self.size - k;
+		self.entries[i:n] = self.entries[k:n];
+		self.size -= k - i;
+		// Find last index of item not to be deleted.
+		while (i > 0 && !m(o, &self.entries[i - 1])) i--;
+		k = i;
 	}
 	return size - self.size;
 }
@@ -255,19 +277,15 @@ fn usz List.remove_if(&self, ElementPredicate filter)
  **/
 fn usz List.retain_if(&self, ElementPredicate selection)
 {
-	usz size = self.size;
-	for (usz i = size; i > 0; i--)
-	{
-		if (!selection(&self.entries[i - 1])) continue;
-		for (usz j = i; j < size; j++)
-		{
-			self.entries[j - 1] = self.entries[j];
-		}
-		self.size--;
-	}
-	return size - self.size;
+	return self._remove_if({ selection }, &Filter.opposite);
 }
 
+struct Filter @private
+{
+	ElementPredicate p;
+}
+fn bool Filter.same(self, Type* type) => self.p(type) @inline;
+fn bool Filter.opposite(self, Type* type) => !self.p(type) @inline;
 
 /**
  * Reserve at least min_capacity
diff --git a/test/unit/stdlib/collections/list.c3 b/test/unit/stdlib/collections/list.c3
index 686d36a26..2531a6dc7 100644
--- a/test/unit/stdlib/collections/list.c3
+++ b/test/unit/stdlib/collections/list.c3
@@ -4,7 +4,7 @@ import std::collections::list;
 def IntList = List(<int>);
 def PtrList = List(<void*>);
 
-fn void! test_delete_contains_index()
+fn void! delete_contains_index()
 {
 	IntList test;
 	test.add_array({ 1, 2 });
@@ -33,7 +33,7 @@ fn void! test_delete_contains_index()
 	assert(test.array_view() == int[]{ 2, 3 });
 }
 
-fn void! test_compact()
+fn void! compact()
 {
 	PtrList test;
 	test.add_array({ null, &test });
@@ -46,7 +46,7 @@ fn void! test_compact()
 	assert(test.compact() == 0);
 }
 
-fn void! test_reverse()
+fn void! reverse()
 {
 	IntList test;
 	test.reverse();
@@ -59,4 +59,50 @@ fn void! test_reverse()
 	assert(test.array_view() == int[] { 3, 2, 1, 10 });
 	test.reverse();
 	assert(test.array_view() == int[] { 10, 1, 2, 3 });
+}
+
+fn void! remove_if()
+{
+	IntList test;
+	usz removed;
+
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_if(&filter);
+	assert(removed == 3);
+	assert(test.array_view() == int[]{1, 2});
+
+	test.clear();
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_if(&select);
+	assert(removed == 2);
+	assert(test.array_view() == int[]{11, 10, 20});
+}
+
+fn void! retain_if()
+{
+	IntList test;
+	usz removed;
+
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.retain_if(&select);
+	assert(removed == 3);
+	assert(test.array_view() == int[]{1, 2});
+
+	test.clear();
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.retain_if(&filter);
+	assert(removed == 2);
+	assert(test.array_view() == int[]{11, 10, 20});
+}
+
+module list_test;
+
+fn bool filter(int* i)
+{
+	return *i >= 10;
+}
+
+fn bool select(int* i)
+{
+	return *i < 10;
 }
\ No newline at end of file