diff --git a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Writers/CodeWriter.cs b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Writers/CodeWriter.cs
index f57b5435a4d..24156f94b49 100644
--- a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Writers/CodeWriter.cs
+++ b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Writers/CodeWriter.cs
@@ -658,8 +658,11 @@ private void AppendType(CSharpType type, bool isDeclaration, bool writeTypeNameO
                 UseNamespace(type.Namespace);
 
                 AppendRaw("global::");
-                AppendRaw(type.Namespace);
-                AppendRaw(".");
+                if (!string.IsNullOrEmpty(type.Namespace))
+                {
+                    AppendRaw(type.Namespace);
+                    AppendRaw(".");
+                }
                 if (type.DeclaringType is not null)
                     AppendRaw($"{type.DeclaringType.Name}.");
                 AppendRaw(type.Name);
diff --git a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Writers/CodeWriterTests.cs b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Writers/CodeWriterTests.cs
index 6fec1f24139..cfa5e02c23e 100644
--- a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Writers/CodeWriterTests.cs
+++ b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Writers/CodeWriterTests.cs
@@ -727,5 +727,54 @@ public void CodeWriter_WriteMethod_AbstractMethodWithoutBody()
             var result = codeWriter.ToString(false);
             Assert.AreEqual(expected, result);
         }
+
+        // Regression test for https://github.com/microsoft/typespec/issues/9880
+        // When a CSharpType has an empty namespace (can happen when Roslyn cannot resolve the type),
+        // the CodeWriter should not output "global::." (global prefix followed by empty namespace and dot).
+        [Test]
+        public void TypeWithEmptyNamespaceDoesNotOutputGlobalDot()
+        {
+            // Create a CSharpType with an empty namespace (simulating an unresolved error type)
+            var typeWithEmptyNamespace = new CSharpType(
+                "UnresolvedType",
+                "", // empty namespace
+                isValueType: false,
+                isNullable: false,
+                declaringType: null,
+                args: [],
+                isPublic: true,
+                isStruct: false);
+
+            using var writer = new CodeWriter();
+            writer.Append($"{typeWithEmptyNamespace}");
+            var result = writer.ToString(false);
+
+            // Should contain "global::UnresolvedType" (without extra dot after global::)
+            Assert.That(result, Does.Contain("global::UnresolvedType"),
+                "Type with empty namespace should be prefixed with 'global::' directly followed by the type name");
+        }
+
+        // Verifies that types with proper namespaces still work correctly
+        [Test]
+        public void TypeWithNamespaceOutputsCorrectly()
+        {
+            var typeWithNamespace = new CSharpType(
+                "ResolvedType",
+                "Sample.Models",
+                isValueType: false,
+                isNullable: false,
+                declaringType: null,
+                args: [],
+                isPublic: true,
+                isStruct: false);
+
+            using var writer = new CodeWriter();
+            writer.Append($"{typeWithNamespace}");
+            var result = writer.ToString(false);
+
+            // Should contain the full qualified name
+            Assert.That(result, Does.Contain("global::Sample.Models.ResolvedType"),
+                "Type with namespace should include the full namespace in output");
+        }
     }
 }