diff --git a/src/ISADotNet.QueryModel/Row.fs b/src/ISADotNet.QueryModel/Row.fs
index a0e870f3..ad6ad566 100644
--- a/src/ISADotNet.QueryModel/Row.fs
+++ b/src/ISADotNet.QueryModel/Row.fs
@@ -107,7 +107,7 @@ type QRow =
             (characteristics |> List.map Characteristic)
             @ (parameters |> List.map Parameter)
             @ (factors |> List.map Factor)
-            |> List.sortBy (fun v -> v.ValueIndex)
+            |> List.sortBy (fun v -> v.TryValueIndex |> Option.defaultValue System.Int32.MaxValue)
 
         {
             Input = Input |> Option.defaultValue ""
diff --git a/src/ISADotNet.QueryModel/Value.fs b/src/ISADotNet.QueryModel/Value.fs
index 3257ff3c..8328b20e 100644
--- a/src/ISADotNet.QueryModel/Value.fs
+++ b/src/ISADotNet.QueryModel/Value.fs
@@ -96,7 +96,16 @@ type ISAValue =
         | Factor f          -> f.ValueWithUnitText
 
     member this.ValueIndex =
+        try
+            match this with
+            | Parameter p       -> p.GetValueIndex()
+            | Characteristic c  -> c.GetValueIndex()
+            | Factor f          -> f.GetValueIndex()
+        with
+        | _ -> failwithf $"Value index could not be retrieved for value {this.NameText}"
+
+    member this.TryValueIndex =
         match this with
-        | Parameter p       -> p.GetValueIndex()
-        | Characteristic c  -> c.GetValueIndex()
-        | Factor f          -> f.GetValueIndex()
\ No newline at end of file
+        | Parameter p       -> p.TryGetValueIndex()
+        | Characteristic c  -> c.TryGetValueIndex()
+        | Factor f          -> f.TryGetValueIndex()
\ No newline at end of file
diff --git a/src/ISADotnet/ValueIndex.fs b/src/ISADotnet/ValueIndex.fs
index 2dbed301..da16c48a 100644
--- a/src/ISADotnet/ValueIndex.fs
+++ b/src/ISADotnet/ValueIndex.fs
@@ -66,12 +66,20 @@ module ValueIndexExtensions =
 
         member this.GetValueIndex() = ValueIndex.tryGetFactorIndex this |> Option.get
 
+        static member tryGetValueIndex(f) = ValueIndex.tryGetFactorIndex f
+
+        member this.TryGetValueIndex() = ValueIndex.tryGetFactorIndex this
+
     type FactorValue with
 
         static member getValueIndex(f) = ValueIndex.tryGetFactorValueIndex f |> Option.get
 
         member this.GetValueIndex() = ValueIndex.tryGetFactorValueIndex this |> Option.get
 
+        static member tryGetValueIndex(f) = ValueIndex.tryGetFactorValueIndex f
+
+        member this.TryGetValueIndex() = ValueIndex.tryGetFactorValueIndex this
+
     type MaterialAttribute with
     
         /// Create a ISAJson characteristic from ISATab string entries
@@ -86,12 +94,20 @@ module ValueIndexExtensions =
 
         member this.GetValueIndex() = ValueIndex.tryGetCharacteristicIndex this |> Option.get
 
+        static member tryGetValueIndex(m) = ValueIndex.tryGetCharacteristicIndex m
+        
+        member this.TryGetValueIndex() = ValueIndex.tryGetCharacteristicIndex this
+
     type MaterialAttributeValue with
             
             static member getValueIndex(m) = ValueIndex.tryGetCharacteristicValueIndex m |> Option.get
 
             member this.GetValueIndex() = ValueIndex.tryGetCharacteristicValueIndex this |> Option.get
 
+            static member tryGetValueIndex(m) = ValueIndex.tryGetCharacteristicValueIndex m
+            
+            member this.TryGetValueIndex() = ValueIndex.tryGetCharacteristicValueIndex this
+
     type ProtocolParameter with
     
         /// Create a ISAJson parameter from ISATab string entries
@@ -106,8 +122,16 @@ module ValueIndexExtensions =
 
         member this.GetValueIndex() = ValueIndex.tryGetParameterIndex this |> Option.get
 
+        static member tryGetValueIndex(p) = ValueIndex.tryGetParameterIndex p
+        
+        member this.TryGetValueIndex() = ValueIndex.tryGetParameterIndex this
+
     type ProcessParameterValue with
     
         static member getValueIndex(p) = ValueIndex.tryGetParameterValueIndex p |> Option.get
 
         member this.GetValueIndex() = ValueIndex.tryGetParameterValueIndex this |> Option.get
+
+        static member tryGetValueIndex(p) = ValueIndex.tryGetParameterValueIndex p
+        
+        member this.TryGetValueIndex() = ValueIndex.tryGetParameterValueIndex this
\ No newline at end of file