diff --git a/release-notes.txt b/release-notes.txt
index 5bd4ac6..7078840 100644
--- a/release-notes.txt
+++ b/release-notes.txt
@@ -2,6 +2,7 @@
 Release notes:
 
 1.0.0
+    - fixes: TaskSeq.insertAt, insertManyAt, removeAt, removeManyAt, updateAt now raise ArgumentNullException (not NullReferenceException) when given a null source; insertManyAt also validates the values argument
     - refactor: simplify lengthBy and lengthBeforeMax to use while! and remove the redundant mutable 'go' and initial MoveNextAsync
     - adds TaskSeq.distinctUntilChangedWith and TaskSeq.distinctUntilChangedWithAsync, #345
     - adds TaskSeq.withCancellation, #167
diff --git a/src/FSharp.Control.TaskSeq.Test/TaskSeq.InsertAt.Tests.fs b/src/FSharp.Control.TaskSeq.Test/TaskSeq.InsertAt.Tests.fs
index ad8a8c8..b198330 100644
--- a/src/FSharp.Control.TaskSeq.Test/TaskSeq.InsertAt.Tests.fs
+++ b/src/FSharp.Control.TaskSeq.Test/TaskSeq.InsertAt.Tests.fs
@@ -16,6 +16,18 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () =
+        assertNullArg <| fun () -> TaskSeq.insertAt 0 99 null
+
+        assertNullArg
+        <| fun () -> TaskSeq.insertManyAt 0 TaskSeq.empty null
+
+    [<Fact>]
+    let ``Null values argument is invalid for insertManyAt`` () =
+        assertNullArg
+        <| fun () -> TaskSeq.insertManyAt 0 null (TaskSeq.ofList [ 1 ])
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-insertAt(0) on empty input returns singleton`` variant =
         Gen.getEmptyVariant variant
diff --git a/src/FSharp.Control.TaskSeq.Test/TaskSeq.RemoveAt.Tests.fs b/src/FSharp.Control.TaskSeq.Test/TaskSeq.RemoveAt.Tests.fs
index 9c60052..56b332e 100644
--- a/src/FSharp.Control.TaskSeq.Test/TaskSeq.RemoveAt.Tests.fs
+++ b/src/FSharp.Control.TaskSeq.Test/TaskSeq.RemoveAt.Tests.fs
@@ -16,6 +16,12 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () =
+        assertNullArg <| fun () -> TaskSeq.removeAt 0 null
+
+        assertNullArg <| fun () -> TaskSeq.removeManyAt 0 1 null
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-removeAt(0) on empty input raises`` variant =
         fun () ->
diff --git a/src/FSharp.Control.TaskSeq.Test/TaskSeq.UpdateAt.Tests.fs b/src/FSharp.Control.TaskSeq.Test/TaskSeq.UpdateAt.Tests.fs
index 0bf7e9d..ed93a48 100644
--- a/src/FSharp.Control.TaskSeq.Test/TaskSeq.UpdateAt.Tests.fs
+++ b/src/FSharp.Control.TaskSeq.Test/TaskSeq.UpdateAt.Tests.fs
@@ -15,6 +15,9 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () = assertNullArg <| fun () -> TaskSeq.updateAt 0 99 null
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-updateAt(0) on empty input should throw ArgumentException`` variant =
         fun () ->
diff --git a/src/FSharp.Control.TaskSeq/TaskSeqInternal.fs b/src/FSharp.Control.TaskSeq/TaskSeqInternal.fs
index bfcddc0..578c6ed 100644
--- a/src/FSharp.Control.TaskSeq/TaskSeqInternal.fs
+++ b/src/FSharp.Control.TaskSeq/TaskSeqInternal.fs
@@ -1369,6 +1369,12 @@ module internal TaskSeqInternal =
 
     /// InsertAt or InsertManyAt
     let insertAt index valueOrValues (source: TaskSeq<_>) =
+        checkNonNull (nameof source) source
+
+        match valueOrValues with
+        | Many values -> checkNonNull "values" values
+        | One _ -> ()
+
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1394,6 +1400,7 @@ module internal TaskSeqInternal =
         }
 
     let removeAt index (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1411,6 +1418,7 @@ module internal TaskSeqInternal =
         }
 
     let removeManyAt index count (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1429,6 +1437,7 @@ module internal TaskSeqInternal =
         }
 
     let updateAt index value (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {