diff --git a/src/FSharpx.Collections/CircularBuffer.fs b/src/FSharpx.Collections/CircularBuffer.fs
index ea44f8db..5359b20b 100644
--- a/src/FSharpx.Collections/CircularBuffer.fs
+++ b/src/FSharpx.Collections/CircularBuffer.fs
@@ -48,17 +48,31 @@ type CircularBuffer<'T>(bufferSize: int) =
         dequeued
 
     member this.Enqueue(value: _[], offset, count) =
+        if isNull value then
+            invalidArg "value" "value must not be null."
+
+        if offset < 0 then
+            invalidArg "offset" "offset must not be negative."
+
+        if count < 0 then
+            invalidArg "count" "count must not be negative."
+
+        if offset + count > value.Length then
+            invalidArg "count" "offset and count exceed the length of the source array."
+
         if count > bufferSize then
             invalidOp "Requested count is too large."
 
         let mutable offset = offset
 
-        head <- (head + 1) % bufferSize
+        let startPos = (head + 1) % bufferSize
 
-        for x, y in nextBuffer head count do
+        for x, y in nextBuffer startPos count do
             Array.blit value offset buffer x y
             offset <- offset + y
 
+        head <- (head + count) % bufferSize
+
         if length = bufferSize then
             tail <- (tail + count) % bufferSize
         else
diff --git a/tests/FSharpx.Collections.Tests/CircularBufferTests.fs b/tests/FSharpx.Collections.Tests/CircularBufferTests.fs
index ae455d44..d371ddc7 100644
--- a/tests/FSharpx.Collections.Tests/CircularBufferTests.fs
+++ b/tests/FSharpx.Collections.Tests/CircularBufferTests.fs
@@ -84,7 +84,34 @@ module CircularBufferTests =
                   Expect.throwsT<System.InvalidOperationException> "" f
               }
 
-              ptest "Printing after multiple enqueue circles" {
+              test "fail on negative offset" {
+                  let f =
+                      fun _ ->
+                          let circularBuffer = CircularBuffer<int> 5
+                          circularBuffer.Enqueue([| 1; 2; 3 |], -1, 2)
+
+                  Expect.throwsT<System.ArgumentException> "" f
+              }
+
+              test "fail on negative count" {
+                  let f =
+                      fun _ ->
+                          let circularBuffer = CircularBuffer<int> 5
+                          circularBuffer.Enqueue([| 1; 2; 3 |], 0, -1)
+
+                  Expect.throwsT<System.ArgumentException> "" f
+              }
+
+              test "fail when offset + count exceeds array length" {
+                  let f =
+                      fun _ ->
+                          let circularBuffer = CircularBuffer<int> 5
+                          circularBuffer.Enqueue([| 1; 2; 3 |], 2, 3)
+
+                  Expect.throwsT<System.ArgumentException> "" f
+              }
+
+              test "Printing after multiple enqueue circles" {
                   let circularBuffer = CircularBuffer<int> 5
 
                   circularBuffer.Enqueue [| 1; 2; 3; 4; 5 |]
@@ -96,7 +123,7 @@ module CircularBufferTests =
 
 
 
-              ptest "Printing from a queue 1..8 and dequeue 5, then enqueue 1..3 and dequeue 3, from array" {
+              test "Printing from a queue 1..8 and dequeue 5, then enqueue 1..3 and dequeue 3, from array" {
                   let circularBuffer = CircularBuffer<int> 5
 
                   circularBuffer.Enqueue([| 1; 2; 3; 4; 5 |])
@@ -106,7 +133,7 @@ module CircularBufferTests =
                   Expect.equal "buffer" [| 1; 2; 3 |] <| circularBuffer.Dequeue 3
               }
 
-              ptest "Consider a large array with various, incoming array segments" {
+              test "Consider a large array with various, incoming array segments" {
                   let circularBuffer = CircularBuffer<int> 5
 
                   let source =