diff --git a/src/Analyzers/CSharp/Tests/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs b/src/Analyzers/CSharp/Tests/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs
index bf6f66a330a77..af603723f36cd 100644
--- a/src/Analyzers/CSharp/Tests/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs
+++ b/src/Analyzers/CSharp/Tests/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs
@@ -9369,6 +9369,29 @@ private static void M(ref int destinationIndex, S buffer)
             ReferenceAssemblies = ReferenceAssemblies.Net.Net80,
         }.RunAsync();
 
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/81554")]
+    public Task TestWriteIntoExtensionRefReceiver()
+        => new VerifyCS.Test
+        {
+            TestCode = """
+                public static class E
+                {
+                    extension(ref double number)
+                    {
+                        public void M(double max)
+                        {
+                            number = max;
+                        }
+                    }
+                }
+                """,
+            LanguageVersion = LanguageVersion.CSharp14,
+            Options =
+            {
+                { CSharpCodeStyleOptions.UnusedValueAssignment, UnusedValuePreference.DiscardVariable, NotificationOption2.Suggestion },
+            },
+        }.RunAsync();
+
     [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/77258")]
     public Task TestWriteIntoStructIndexer()
         => new VerifyCS.Test
diff --git a/src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/FlowAnalysis/SymbolUsageAnalysis/SymbolUsageAnalysis.DataFlowAnalyzer.FlowGraphAnalysisData.cs b/src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/FlowAnalysis/SymbolUsageAnalysis/SymbolUsageAnalysis.DataFlowAnalyzer.FlowGraphAnalysisData.cs
index fa5d00eb49c1b..5a5b53deedcf5 100644
--- a/src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/FlowAnalysis/SymbolUsageAnalysis/SymbolUsageAnalysis.DataFlowAnalyzer.FlowGraphAnalysisData.cs
+++ b/src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/FlowAnalysis/SymbolUsageAnalysis/SymbolUsageAnalysis.DataFlowAnalyzer.FlowGraphAnalysisData.cs
@@ -120,7 +120,8 @@ public static FlowGraphAnalysisData Create(
             {
                 Debug.Assert(cfg.Parent == null);
 
-                var parameters = owningSymbol.GetParameters();
+                var parameters = GetParameters(owningSymbol);
+
                 return new FlowGraphAnalysisData(
                     cfg,
                     owningSymbol,
@@ -134,6 +135,21 @@ public static FlowGraphAnalysisData Create(
                     reachingDelegateCreationTargets: PooledDictionary<IOperation, PooledHashSet<IOperation>>.GetInstance(),
                     localFunctionTargetsToAccessingCfgMap: PooledDictionary<IMethodSymbol, ControlFlowGraph>.GetInstance(),
                     lambdaTargetsToAccessingCfgMap: PooledDictionary<IFlowAnonymousFunctionOperation, ControlFlowGraph>.GetInstance());
+
+                static ImmutableArray<IParameterSymbol> GetParameters(ISymbol owningSymbol)
+                {
+                    var parameters = owningSymbol.GetParameters();
+#if !ROSLYN_4_12_OR_LOWER
+                    if (owningSymbol.ContainingSymbol is INamedTypeSymbol { IsExtension: true, ExtensionParameter: { } extensionParameter })
+                    {
+                        return parameters.Add(extensionParameter); // order doesn't matter
+                    }
+
+                    return parameters;
+#else
+                    return parameters;
+#endif
+                }
             }
 
             public static FlowGraphAnalysisData Create(