diff --git a/src/Compiler/Utilities/range.fs b/src/Compiler/Utilities/range.fs
index 09633136dbe..f9940461a32 100755
--- a/src/Compiler/Utilities/range.fs
+++ b/src/Compiler/Utilities/range.fs
@@ -196,31 +196,29 @@ type FileIndexTable() =
         match fileToIndexTable.TryGetValue filePath with
         | true, idx -> idx
         | _ ->
-            // If a write operation can happen, we have to lock the whole read-check-write to avoid race conditions
-            lock fileToIndexTable
-            <| fun () ->
-                match fileToIndexTable.TryGetValue filePath with
-                | true, idx -> idx
-                | _ ->
-
-                    // Try again looking for a normalized entry.
-                    let normalizedFilePath =
-                        if normalize then
-                            FileSystem.NormalizePathShim filePath
-                        else
-                            filePath
+            // Try again looking for a normalized entry.
+            let normalizedFilePath =
+                if normalize then
+                    FileSystem.NormalizePathShim filePath
+                else
+                    filePath
 
-                    match fileToIndexTable.TryGetValue normalizedFilePath with
-                    | true, idx ->
-                        // Record the non-normalized entry if necessary
-                        if filePath <> normalizedFilePath then
-                            fileToIndexTable[filePath] <- idx
+            match fileToIndexTable.TryGetValue normalizedFilePath with
+            | true, idx ->
+                // Record the non-normalized entry if necessary
+                if filePath <> normalizedFilePath then
+                    fileToIndexTable[filePath] <- idx
 
-                        // Return the index
-                        idx
+                // Return the index
+                idx
 
+            | _ ->
+                lock indexToFileTable (fun () ->
+                    // See if it was added on another thread
+                    match fileToIndexTable.TryGetValue normalizedFilePath with
+                    | true, idx -> idx
                     | _ ->
-                        // Get the new index
+                        // Okay it's really not there
                         let idx = indexToFileTable.Count
 
                         // Record the normalized entry
@@ -232,7 +230,7 @@ type FileIndexTable() =
                             fileToIndexTable[filePath] <- idx
 
                         // Return the index
-                        idx
+                        idx)
 
     member t.IndexToFile n =
         if n < 0 then
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
index 03328728f4c..7753d4d453f 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
@@ -59,7 +59,7 @@
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x0000000B][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x00000021][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000CD][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@546::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000037][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000043][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
index a863787a54e..c08ff170540 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
@@ -84,7 +84,7 @@
 [IL]: Error [StackUnexpected]: : Internal.Utilities.FSharpEnvironment+probePathForDotnetHost@321::Invoke([FSharp.Core]Microsoft.FSharp.Core.Unit)][offset 0x00000028][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.CodeAnalysis.SimulatedMSBuildReferenceResolver+Pipe #6 input at line 68@68::FSharp.Compiler.CodeAnalysis.ILegacyReferenceResolver.Resolve([FSharp.Compiler.Service]FSharp.Compiler.CodeAnalysis.LegacyResolutionEnvironment, [S.P.CoreLib]System.Tuple`2<string,string>[], string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1<string>, string, string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1<string>, string, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.Unit>, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<bool,Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.Unit>>>)][offset 0x0000034D][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000CD][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@546::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000037][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000043][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
index d1f7525cef2..e40fe8f5802 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
@@ -85,7 +85,7 @@
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x0000000B][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x00000021][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000B6][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@546::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000035][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000041][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
index 9de22b5cd79..ba85c0b42c0 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
@@ -111,7 +111,7 @@
 [IL]: Error [StackUnexpected]: : Internal.Utilities.FSharpEnvironment::probePathForDotnetHost@320([FSharp.Core]Microsoft.FSharp.Core.Unit)][offset 0x0000002A][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : FSharp.Compiler.CodeAnalysis.SimulatedMSBuildReferenceResolver+SimulatedMSBuildResolver@68::FSharp.Compiler.CodeAnalysis.ILegacyReferenceResolver.Resolve([FSharp.Compiler.Service]FSharp.Compiler.CodeAnalysis.LegacyResolutionEnvironment, [S.P.CoreLib]System.Tuple`2<string,string>[], string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1<string>, string, string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1<string>, string, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.Unit>, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2<bool,Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.FSharpFunc`2<string,Microsoft.FSharp.Core.Unit>>>)][offset 0x000002F5][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000B6][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@546::System.Collections.Generic.IEqualityComparer<FSharp.Compiler.Text.Range>.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000035][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000041][found Char] Unexpected type on the stack.
 [IL]: Error [StackUnexpected]: : <StartupCode$FSharp-Compiler-Service>.$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.