diff --git a/src/Analyzers/Orchestration/OrchestrationAnalyzer.cs b/src/Analyzers/Orchestration/OrchestrationAnalyzer.cs
index ca36af86..a299d577 100644
--- a/src/Analyzers/Orchestration/OrchestrationAnalyzer.cs
+++ b/src/Analyzers/Orchestration/OrchestrationAnalyzer.cs
@@ -316,7 +316,12 @@ void FindInvokedMethods(
             IEnumerable<MethodDeclarationSyntax> calleeSyntaxes = calleeMethodSymbol.GetSyntaxNodes();
             foreach (MethodDeclarationSyntax calleeSyntax in calleeSyntaxes)
             {
-                this.FindInvokedMethods(semanticModel, calleeSyntax, calleeMethodSymbol, rootOrchestration, reportDiagnostic);
+                // Since the syntax tree of the callee method might be different from the caller method, we need to get the correct semantic model,
+                // avoiding the exception 'Syntax node is not within syntax tree'.
+                SemanticModel sm = semanticModel.SyntaxTree == calleeSyntax.SyntaxTree ?
+                    semanticModel : semanticModel.Compilation.GetSemanticModel(calleeSyntax.SyntaxTree);
+
+                this.FindInvokedMethods(sm, calleeSyntax, calleeMethodSymbol, rootOrchestration, reportDiagnostic);
             }
         }
     }
diff --git a/test/Analyzers.Tests/Orchestration/DateTimeOrchestrationAnalyzerTests.cs b/test/Analyzers.Tests/Orchestration/DateTimeOrchestrationAnalyzerTests.cs
index 77bfc515..18a90349 100644
--- a/test/Analyzers.Tests/Orchestration/DateTimeOrchestrationAnalyzerTests.cs
+++ b/test/Analyzers.Tests/Orchestration/DateTimeOrchestrationAnalyzerTests.cs
@@ -222,6 +222,32 @@ public class MyOrchestrator : ITaskOrchestrator
         await VerifyCS.VerifyDurableTaskAnalyzerAsync(code, expected);
     }
 
+    [Fact]
+    public async Task TaskOrchestratorUsingDifferentSyntaxTreesHasDiag()
+    {
+        string mainCode = Wrapper.WrapTaskOrchestrator(@"
+public class MyOrchestrator : TaskOrchestrator<string, DateTime>
+{
+    public override Task<DateTime> RunAsync(TaskOrchestrationContext context, string input)
+    {
+        var dependency = new Dependency();
+        return Task.FromResult(dependency.Method());
+    }
+}
+");
+        string codeInAnotherSyntaxTree = Wrapper.WrapTaskOrchestrator(@"
+public class Dependency{
+    public DateTime Method() => {|#0:DateTime.Now|};
+}
+");
+
+        void configureTest(VerifyCS.Test test) => test.TestState.Sources.Add(codeInAnotherSyntaxTree);
+
+        DiagnosticResult expected = BuildDiagnostic().WithLocation(0).WithArguments("Method", "System.DateTime.Now", "MyOrchestrator");
+
+        await VerifyCS.VerifyDurableTaskAnalyzerAsync(mainCode, configureTest, expected);
+    }
+
 
     [Fact]
     public async Task FuncOrchestratorWithLambdaHasDiag()
diff --git a/test/Analyzers.Tests/Verifiers/CSharpAnalyzerVerifier.Durable.cs b/test/Analyzers.Tests/Verifiers/CSharpAnalyzerVerifier.Durable.cs
index 89a1178a..6d035e77 100644
--- a/test/Analyzers.Tests/Verifiers/CSharpAnalyzerVerifier.Durable.cs
+++ b/test/Analyzers.Tests/Verifiers/CSharpAnalyzerVerifier.Durable.cs
@@ -12,6 +12,11 @@ public static partial class CSharpAnalyzerVerifier<TAnalyzer>
 {
     /// <inheritdoc cref="AnalyzerVerifier{TAnalyzer, TTest, TVerifier}.VerifyAnalyzerAsync(string, DiagnosticResult[])"/>
     public static async Task VerifyDurableTaskAnalyzerAsync(string source, params DiagnosticResult[] expected)
+    {
+        await VerifyDurableTaskAnalyzerAsync(source, null, expected);
+    }
+
+    public static async Task VerifyDurableTaskAnalyzerAsync(string source, Action<Test>? configureTest = null, params DiagnosticResult[] expected)
     {
         Test test = new()
         {
@@ -24,6 +29,8 @@ public static async Task VerifyDurableTaskAnalyzerAsync(string source, params Di
 
         test.ExpectedDiagnostics.AddRange(expected);
 
+        configureTest?.Invoke(test);
+
         await test.RunAsync(CancellationToken.None);
     }
 }