diff --git a/src/main/java/com/annimon/ownlang/lib/modules/functions/functional_stream.java b/src/main/java/com/annimon/ownlang/lib/modules/functions/functional_stream.java
index ea5fd1e..aac8408 100644
--- a/src/main/java/com/annimon/ownlang/lib/modules/functions/functional_stream.java
+++ b/src/main/java/com/annimon/ownlang/lib/modules/functions/functional_stream.java
@@ -29,7 +29,7 @@ public final class functional_stream implements Function {
         private final ArrayValue container;
 
         public StreamValue(ArrayValue container) {
-            super(12);
+            super(13);
             this.container = container;
             init();
         }
@@ -43,6 +43,7 @@ public final class functional_stream implements Function {
             set("dropWhile", wrapIntermediate(new functional_dropwhile()));
             set("skip", this::skip);
             set("limit", this::limit);
+            set("custom", this::custom);
 
             set("reduce", wrapTerminal(new functional_reduce()));
             set("forEach", wrapTerminal(new functional_foreach()));
@@ -82,6 +83,19 @@ public final class functional_stream implements Function {
             return new StreamValue(new ArrayValue(result));
         }
 
+        private Value custom(Value... args) {
+            Arguments.check(1, args.length);
+            if (args[0].type() != Types.FUNCTION) {
+                throw new TypeException("Function expected in first argument");
+            }
+            final Function f = ((FunctionValue) args[0]).getValue();
+            final Value result = f.execute(container);
+            if (result.type() == Types.ARRAY) {
+                return new StreamValue((ArrayValue) result);
+            }
+            return result;
+        }
+
         private FunctionValue wrapIntermediate(Function f) {
             return wrap(f, true);
         }
diff --git a/src/test/resources/modules/functional/stream.own b/src/test/resources/modules/functional/stream.own
index 48647c2..19fa66d 100644
--- a/src/test/resources/modules/functional/stream.own
+++ b/src/test/resources/modules/functional/stream.own
@@ -1,3 +1,4 @@
+use "std"
 use "functional"
 
 def testStream() {
@@ -37,3 +38,17 @@ def testDropWhile() {
   assertEquals([5, 6, 7, 8], stream(data).dropWhile(def(x) = x % 2 == 0).toArray())
   assertEquals(data, stream(data).dropWhile(def(x) = x % 2 != 0).toArray())
 }
+
+def testCustom() {
+  data = [2,4,6,5]
+  assertEquals([5,6,4,2], stream(data).custom(::reverse).toArray())
+}
+
+def reverse(container) {
+  size = length(container)
+  result = newarray(size)
+  for i : range(size) {
+    result[size - i - 1] = container[i]
+  }
+  return result
+}
\ No newline at end of file