diff --git a/src/FSharpPlus/Control/Monad.fs b/src/FSharpPlus/Control/Monad.fs
index 2260364ec..89172e518 100644
--- a/src/FSharpPlus/Control/Monad.fs
+++ b/src/FSharpPlus/Control/Monad.fs
@@ -50,13 +50,29 @@ type Bind =
                        | Some v -> yield k, v
                        | _      -> () })
 
-    static member (>>=) (source: Dictionary<'Key,'T>, f: 'T -> Dictionary<'Key,'U>) = 
-                   let dct = Dictionary ()
-                   for KeyValue(k, v) in source do
-                       match (f v).TryGetValue (k) with
-                       | true, v -> dct.Add (k, v)
-                       | _       -> ()
-                   dct
+    static member (>>=) (source: Dictionary<'Key,'T>, f: 'T -> Dictionary<'Key,'U>) =
+               let dct = Dictionary ()
+               for KeyValue(k, v) in source do
+                   match (f v).TryGetValue (k) with
+                   | true, v -> dct.Add (k, v)
+                   | _       -> ()
+               dct
+
+    static member (>>=) (source: IDictionary<'Key,'T>, f: 'T -> IDictionary<'Key,'U>) =
+               let dct = Dictionary ()
+               for KeyValue(k, v) in source do
+                   match (f v).TryGetValue (k) with
+                   | true, v -> dct.Add (k, v)
+                   | _       -> ()
+               dct :> IDictionary<'Key,'U>
+
+    static member (>>=) (source: IReadOnlyDictionary<'Key,'T>, f: 'T -> IReadOnlyDictionary<'Key,'U>) =
+               let dct = Dictionary ()
+               for KeyValue(k, v) in source do
+                   match (f v).TryGetValue (k) with
+                   | true, v -> dct.Add (k, v)
+                   | _       -> ()
+               dct :> IReadOnlyDictionary<'Key,'U>
 
     static member (>>=) (source: ResizeArray<'T>, f: 'T -> ResizeArray<'U>) = ResizeArray (Seq.bind (f >> seq<_>) source) : ResizeArray<'U>
 
@@ -114,6 +130,22 @@ type Join =
                         | _       -> ()
                     dct
 
+    static member Join (x: IDictionary<_, IDictionary<_, _>>, [<Optional>]_output: IDictionary<'Key, 'Value>, [<Optional>]_mthd: Join) : IDictionary<'Key, 'Value> =
+        let dct = Dictionary ()
+        for KeyValue(k, v) in x do
+            match v.TryGetValue (k)  with
+            | true, v -> dct.Add (k, v)
+            | _       -> ()
+        dct :> IDictionary<'Key, 'U>
+
+    static member Join (x: IReadOnlyDictionary<_, IReadOnlyDictionary<_, _>>, [<Optional>]_output: IReadOnlyDictionary<'Key, 'Value>, [<Optional>]_mthd: Join) : IReadOnlyDictionary<'Key, 'Value> =
+        let dct = Dictionary ()
+        for KeyValue(k, v) in x do
+            match v.TryGetValue (k)  with
+            | true, v -> dct.Add (k, v)
+            | _       -> ()
+        dct :> IReadOnlyDictionary<'Key, 'U>
+
     static member        Join (x: ResizeArray<ResizeArray<'T>> , [<Optional>]_output: ResizeArray<'T>        , [<Optional>]_mthd: Join) = ResizeArray (Seq.bind seq<_> x) : ResizeArray<'T> 
     
     static member        Join (x: NonEmptySeq<NonEmptySeq<'T>> , [<Optional>]_output: NonEmptySeq<'T>        , [<Optional>]_mthd: Join) = NonEmptySeq.concat x : NonEmptySeq<'T> 
diff --git a/tests/FSharpPlus.Tests/FSharpPlus.Tests.fsproj b/tests/FSharpPlus.Tests/FSharpPlus.Tests.fsproj
index 734bf6e45..b9dfcf836 100644
--- a/tests/FSharpPlus.Tests/FSharpPlus.Tests.fsproj
+++ b/tests/FSharpPlus.Tests/FSharpPlus.Tests.fsproj
@@ -19,6 +19,7 @@
     <Compile Include="Data.fs" />
     <Compile Include="General.fs" />
     <Compile Include="Applicatives.fs" />
+    <Compile Include="Monads.fs" />
     <Compile Include="Splits.fs" />
     <Compile Include="Monoid.fs" />
     <Compile Include="Parsing.fs" />
diff --git a/tests/FSharpPlus.Tests/General.fs b/tests/FSharpPlus.Tests/General.fs
index 97d0d522c..62da5a027 100644
--- a/tests/FSharpPlus.Tests/General.fs
+++ b/tests/FSharpPlus.Tests/General.fs
@@ -1089,30 +1089,6 @@ module IdiomBrackets =
         let res3n4''' = iI (+) (result 2) [1;2] Ii   // fails to compile when constraints are not properly defined
         Assert.AreEqual ([3;4], res3n4'' )
         Assert.AreEqual ([3;4], res3n4''')
-
-
-        let output = System.Text.StringBuilder ()
-        let append (x: string) = output.Append x |> ignore
-
-        let v5: Lazy<_> = lazy (append "5"; 5)
-        Assert.AreEqual (0, output.Length)
-        let fPlus10 x   = lazy (append " + 10"; x + 10)
-        Assert.AreEqual (0, output.Length)
-        let v5plus10    = v5 >>= fPlus10
-        Assert.AreEqual (0, output.Length)
-        let v15 = v5plus10.Force ()
-        Assert.AreEqual ("5 + 10", string output)
-        Assert.AreEqual (15, v15)
-
-        output.Clear () |> ignore
-
-        let v4ll: Lazy<_> = lazy (append "outer"; lazy (append "inner"; 4))
-        Assert.AreEqual (0, output.Length)
-        let v4l = join v4ll
-        Assert.AreEqual (0, output.Length)
-        let v4  = v4l.Force()
-        Assert.AreEqual ("outerinner", string output)
-        Assert.AreEqual (4, v4)
  
 
 module Alternative =
diff --git a/tests/FSharpPlus.Tests/Monads.fs b/tests/FSharpPlus.Tests/Monads.fs
new file mode 100644
index 000000000..23c0e9901
--- /dev/null
+++ b/tests/FSharpPlus.Tests/Monads.fs
@@ -0,0 +1,43 @@
+namespace FSharpPlus.Tests
+
+open System
+open System.Collections.ObjectModel
+open FSharpPlus
+open FSharpPlus.Data
+open NUnit.Framework
+open Helpers
+
+module Monads =
+    
+    [<Test>]
+    let lazies () =
+        let output = System.Text.StringBuilder ()
+        let append (x: string) = output.Append x |> ignore
+
+        let v5: Lazy<_> = lazy (append "5"; 5)
+        Assert.AreEqual (0, output.Length)
+        let fPlus10 x   = lazy (append " + 10"; x + 10)
+        Assert.AreEqual (0, output.Length)
+        let v5plus10    = v5 >>= fPlus10
+        Assert.AreEqual (0, output.Length)
+        let v15 = v5plus10.Force ()
+        Assert.AreEqual ("5 + 10", string output)
+        Assert.AreEqual (15, v15)
+
+        output.Clear () |> ignore
+
+        let v4ll: Lazy<_> = lazy (append "outer"; lazy (append "inner"; 4))
+        Assert.AreEqual (0, output.Length)
+        let v4l = join v4ll
+        Assert.AreEqual (0, output.Length)
+        let v4  = v4l.Force()
+        Assert.AreEqual ("outerinner", string output)
+        Assert.AreEqual (4, v4)
+
+    [<Test>]
+    let mapLikes () =
+        let r1 = dict [ "a", 1; "b", 2 ; "c", 3 ] >>= fun x -> dict [ "a", x + 10; "c", x + 300; "d", x + 400 ]
+        CollectionAssert.AreEqual (dict [ "a", 11; "c", 303 ], r1)
+
+        let r2 = readOnlyDict [ "a", 1; "b", 2 ; "c", 3 ] >>= fun x -> readOnlyDict [ "a", x + 10; "c", x + 300; "d", x + 400 ]
+        CollectionAssert.AreEqual (readOnlyDict [ "a", 11; "c", 303 ], r2)