diff --git a/src/Meziantou.Analyzer/Rules/StringFormatShouldBeConstantAnalyzer.cs b/src/Meziantou.Analyzer/Rules/StringFormatShouldBeConstantAnalyzer.cs
index ec394a99..bcb1aa66 100644
--- a/src/Meziantou.Analyzer/Rules/StringFormatShouldBeConstantAnalyzer.cs
+++ b/src/Meziantou.Analyzer/Rules/StringFormatShouldBeConstantAnalyzer.cs
@@ -143,8 +143,8 @@ private static bool HasFormattingArguments(IInvocationOperation operation, int f
             }
 #endif
 
-            // Skip other implicit arguments
-            if (arg.IsImplicit)
+            // Skip arguments that were not explicitly provided (e.g. default values)
+            if (arg.ArgumentKind is ArgumentKind.DefaultValue)
                 continue;
 
             return true;
diff --git a/tests/Meziantou.Analyzer.Test/Rules/StringFormatShouldBeConstantAnalyzerTests.cs b/tests/Meziantou.Analyzer.Test/Rules/StringFormatShouldBeConstantAnalyzerTests.cs
index 05b9eb6c..e976d3f4 100644
--- a/tests/Meziantou.Analyzer.Test/Rules/StringFormatShouldBeConstantAnalyzerTests.cs
+++ b/tests/Meziantou.Analyzer.Test/Rules/StringFormatShouldBeConstantAnalyzerTests.cs
@@ -734,4 +734,44 @@ void Method()
                 """)
             .ValidateAsync();
     }
+
+    [Fact]
+    public async Task StringFormat_WithParenthesizedArgAndPlaceholder_ShouldNotReportDiagnostic()
+    {
+        await CreateProjectBuilder()
+            .WithSourceCode("""
+                using System;
+                using System.Globalization;
+
+                class Test
+                {
+                    void Method(object obj)
+                    {
+                        _ = string.Format(CultureInfo.InvariantCulture, "Format string with placeholder: '{0}'.", (obj is null ? string.Empty : "X"));
+                    }
+                }
+                """)
+            .WithTargetFramework(Helpers.TargetFramework.Net10_0)
+            .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task StringFormat_WithParenthesizedArgAndNoPlaceholder_ShouldReportDiagnostic()
+    {
+        await CreateProjectBuilder()
+            .WithSourceCode("""
+                using System;
+                using System.Globalization;
+
+                class Test
+                {
+                    void Method(object obj)
+                    {
+                        _ = [|string.Format(CultureInfo.InvariantCulture, "Format string without placeholder.", (obj is null ? string.Empty : "X"))|];
+                    }
+                }
+                """)
+            .WithTargetFramework(Helpers.TargetFramework.Net10_0)
+            .ValidateAsync();
+    }
 }