diff --git a/WoofWare.Expect/Library.fs b/WoofWare.Expect/Library.fs
index 58641f3..2bfc555 100644
--- a/WoofWare.Expect/Library.fs
+++ b/WoofWare.Expect/Library.fs
@@ -15,6 +15,10 @@ type private SnapshotValue =
     | BareString of string
     | Json of string
 
+/// A dummy type which is here to provide better error messages when you supply
+/// the `snapshot` keyword multiple times.
+type YouHaveSuppliedMultipleSnapshots = private | NonConstructible
+
 /// The state accumulated by the `expect` builder. You should never find yourself interacting with this type.
 type ExpectState<'T> =
     private
@@ -35,7 +39,10 @@ module private Text =
 /// <param name="sourceOverride">Override the file path and line numbers reported in snapshots, so that your tests can be fully stable even on failure. (You almost certainly don't want to set this.)</param>
 type ExpectBuilder (?sourceOverride : string * int) =
     /// Combine two `ExpectState`s. The first one is the "expected" snapshot; the second is the "actual".
-    member _.Bind (state : ExpectState<unit>, f : unit -> ExpectState<'U>) : ExpectState<'U> =
+    member _.Bind
+        (state : ExpectState<YouHaveSuppliedMultipleSnapshots>, f : unit -> ExpectState<'U>)
+        : ExpectState<'U>
+        =
         let actual = f ()
 
         match state.Actual with
@@ -56,13 +63,13 @@ type ExpectBuilder (?sourceOverride : string * int) =
     [<CustomOperation("snapshot", MaintainsVariableSpaceUsingBind = true)>]
     member _.Snapshot
         (
-            state : ExpectState<'a>,
+            state : ExpectState<unit>,
             snapshot : string,
             [<CallerMemberName>] ?memberName : string,
             [<CallerLineNumber>] ?callerLine : int,
             [<CallerFilePath>] ?filePath : string
         )
-        : ExpectState<'a>
+        : ExpectState<YouHaveSuppliedMultipleSnapshots>
         =
         match state.Snapshot with
         | Some _ -> failwith "snapshot can only be specified once"
@@ -78,8 +85,9 @@ type ExpectBuilder (?sourceOverride : string * int) =
                     LineNumber = lineNumber
                 }
 
-            { state with
+            {
                 Snapshot = Some (SnapshotValue.BareString snapshot, callerInfo)
+                Actual = None
             }
 
     /// <summary>
@@ -92,13 +100,13 @@ type ExpectBuilder (?sourceOverride : string * int) =
     [<CustomOperation("snapshotJson", MaintainsVariableSpaceUsingBind = true)>]
     member _.SnapshotJson
         (
-            state : ExpectState<'a>,
+            state : ExpectState<unit>,
             snapshot : string,
             [<CallerMemberName>] ?memberName : string,
             [<CallerLineNumber>] ?callerLine : int,
             [<CallerFilePath>] ?filePath : string
         )
-        : ExpectState<'a>
+        : ExpectState<YouHaveSuppliedMultipleSnapshots>
         =
         match state.Snapshot with
         | Some _ -> failwith "snapshot can only be specified once"
@@ -114,8 +122,9 @@ type ExpectBuilder (?sourceOverride : string * int) =
                     LineNumber = lineNumber
                 }
 
-            { state with
+            {
                 Snapshot = Some (SnapshotValue.Json snapshot, callerInfo)
+                Actual = None
             }
 
     /// MaintainsVariableSpaceUsingBind causes this to be used; it's a dummy representing "no snapshot and no assertion".
diff --git a/WoofWare.Expect/SurfaceBaseline.txt b/WoofWare.Expect/SurfaceBaseline.txt
index 06fe417..5d8e006 100644
--- a/WoofWare.Expect/SurfaceBaseline.txt
+++ b/WoofWare.Expect/SurfaceBaseline.txt
@@ -4,12 +4,14 @@ WoofWare.Expect.Builder.expectWithMockedFilePath [static method]: (string, int)
 WoofWare.Expect.Builder.get_expect [static method]: unit -> WoofWare.Expect.ExpectBuilder
 WoofWare.Expect.ExpectBuilder inherit obj
 WoofWare.Expect.ExpectBuilder..ctor [constructor]: (string * int) option
-WoofWare.Expect.ExpectBuilder.Bind [method]: (unit WoofWare.Expect.ExpectState, unit -> 'U WoofWare.Expect.ExpectState) -> 'U WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.Bind [method]: (WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState, unit -> 'U WoofWare.Expect.ExpectState) -> 'U WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Delay [method]: (unit -> 'T WoofWare.Expect.ExpectState) -> (unit -> 'T WoofWare.Expect.ExpectState)
 WoofWare.Expect.ExpectBuilder.Return [method]: 'T -> 'T WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Return [method]: unit -> 'T WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectBuilder.Run [method]: (unit -> 'T WoofWare.Expect.ExpectState) -> unit
-WoofWare.Expect.ExpectBuilder.Snapshot [method]: ('a WoofWare.Expect.ExpectState, string, string option, int option, string option) -> 'a WoofWare.Expect.ExpectState
-WoofWare.Expect.ExpectBuilder.SnapshotJson [method]: ('a WoofWare.Expect.ExpectState, string, string option, int option, string option) -> 'a WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.Snapshot [method]: (unit WoofWare.Expect.ExpectState, string, string option, int option, string option) -> WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState
+WoofWare.Expect.ExpectBuilder.SnapshotJson [method]: (unit WoofWare.Expect.ExpectState, string, string option, int option, string option) -> WoofWare.Expect.YouHaveSuppliedMultipleSnapshots WoofWare.Expect.ExpectState
 WoofWare.Expect.ExpectState`1 inherit obj, implements 'T WoofWare.Expect.ExpectState System.IEquatable, System.Collections.IStructuralEquatable, 'T WoofWare.Expect.ExpectState System.IComparable, System.IComparable, System.Collections.IStructuralComparable
-WoofWare.Expect.ExpectState`1.Equals [method]: ('T WoofWare.Expect.ExpectState, System.Collections.IEqualityComparer) -> bool
\ No newline at end of file
+WoofWare.Expect.ExpectState`1.Equals [method]: ('T WoofWare.Expect.ExpectState, System.Collections.IEqualityComparer) -> bool
+WoofWare.Expect.YouHaveSuppliedMultipleSnapshots inherit obj, implements WoofWare.Expect.YouHaveSuppliedMultipleSnapshots System.IEquatable, System.Collections.IStructuralEquatable, WoofWare.Expect.YouHaveSuppliedMultipleSnapshots System.IComparable, System.IComparable, System.Collections.IStructuralComparable
+WoofWare.Expect.YouHaveSuppliedMultipleSnapshots.Equals [method]: (WoofWare.Expect.YouHaveSuppliedMultipleSnapshots, System.Collections.IEqualityComparer) -> bool
\ No newline at end of file