diff --git a/Compilation/ILCompiler.Modules.cs b/Compilation/ILCompiler.Modules.cs
index 09b4c572..1e64e534 100644
--- a/Compilation/ILCompiler.Modules.cs
+++ b/Compilation/ILCompiler.Modules.cs
@@ -713,6 +713,14 @@ private void EmitModulesEntryPoint(List<ParsedModule> modules)
             }
         }
 
+        // Initialize namespace static fields before any module/script $Initialize body runs.
+        // Namespace objects live in flat static fields ($ns_*) on $Program shared across every
+        // module, but a module's $Initialize only POPULATES them (EmitNamespace does
+        // $ns_X.Set(...)); it never creates them. The single-file entry point calls this at the
+        // top of Main; the multi-module entry point must too, or the first Set() dereferences a
+        // null namespace field (#1245).
+        InitializeNamespaceFields(il);
+
         // Call each module/script's $Initialize method in dependency order.
         // CommonJS modules are initialized lazily — only the entry CJS module is run eagerly,
         // and require() triggers the rest. This matches Node semantics for the visible execution
diff --git a/SharpTS.Tests/SharedTests/NamespaceInModuleTests.cs b/SharpTS.Tests/SharedTests/NamespaceInModuleTests.cs
new file mode 100644
index 00000000..ca8cd36f
--- /dev/null
+++ b/SharpTS.Tests/SharedTests/NamespaceInModuleTests.cs
@@ -0,0 +1,104 @@
+using SharpTS.Tests.Infrastructure;
+using Xunit;
+
+namespace SharpTS.Tests.SharedTests;
+
+/// <summary>
+/// Regression tests for #1245: in compiled mode, a <c>namespace</c> declaration combined with a
+/// top-level <c>import</c> (which turns the file into an ES module) crashed at startup with a
+/// <c>NullReferenceException</c> in <c>$TSNamespace.Set</c>. The multi-module entry point never
+/// called <c>InitializeNamespaceFields</c>, so the namespace's backing static field was still null
+/// when the module's <c>$Initialize</c> body tried to populate it. A namespace in a plain script
+/// (no import) was unaffected — becoming an ES module is what broke it. The interpreter always ran
+/// these correctly; each test runs both modes so the compiled path is pinned against that oracle.
+/// </summary>
+public class NamespaceInModuleTests
+{
+    [Theory]
+    [MemberData(nameof(ExecutionModes.All), MemberType = typeof(ExecutionModes))]
+    public void Namespace_WithImportAfter_ExportedConst(ExecutionMode mode)
+    {
+        var files = new Dictionary<string, string>
+        {
+            ["main.ts"] = """
+                namespace NS {
+                  export const x = 1;
+                }
+                console.log(NS.x);
+                import * as fs from "fs";
+                console.log(typeof fs.statSync);
+                """
+        };
+        var output = TestHarness.RunModules(files, "main.ts", mode);
+        Assert.Equal("1\nfunction\n", output);
+    }
+
+    [Theory]
+    [MemberData(nameof(ExecutionModes.All), MemberType = typeof(ExecutionModes))]
+    public void Namespace_WithImportBefore_ExportedFunction(ExecutionMode mode)
+    {
+        var files = new Dictionary<string, string>
+        {
+            ["main.ts"] = """
+                import * as path from "path";
+                namespace NS {
+                  export function greet(): string { return "hi"; }
+                }
+                console.log(NS.greet());
+                console.log(typeof path.join);
+                """
+        };
+        var output = TestHarness.RunModules(files, "main.ts", mode);
+        Assert.Equal("hi\nfunction\n", output);
+    }
+
+    [Theory]
+    [MemberData(nameof(ExecutionModes.All), MemberType = typeof(ExecutionModes))]
+    public void NestedNamespace_WithImport(ExecutionMode mode)
+    {
+        var files = new Dictionary<string, string>
+        {
+            ["main.ts"] = """
+                import * as path from "path";
+                namespace Outer {
+                  export const a = 10;
+                  export namespace Inner {
+                    export const b = 42;
+                  }
+                }
+                console.log(Outer.a);
+                console.log(Outer.Inner.b);
+                console.log(typeof path.join);
+                """
+        };
+        var output = TestHarness.RunModules(files, "main.ts", mode);
+        Assert.Equal("10\n42\nfunction\n", output);
+    }
+
+    [Theory]
+    [MemberData(nameof(ExecutionModes.All), MemberType = typeof(ExecutionModes))]
+    public void Namespace_WithSiblingModuleImport_ClassAndEnumMembers(ExecutionMode mode)
+    {
+        var files = new Dictionary<string, string>
+        {
+            ["helper.ts"] = """
+                export function add(a: number, b: number): number { return a + b; }
+                """,
+            ["main.ts"] = """
+                import { add } from "./helper";
+                namespace Calc {
+                  export const base = 10;
+                  export function compute(): number { return add(base, 5); }
+                  export enum Op { Add, Sub }
+                  export class Adder { run(): number { return add(1, 2); } }
+                }
+                console.log(Calc.base);
+                console.log(Calc.compute());
+                console.log(Calc.Op.Sub);
+                console.log(new Calc.Adder().run());
+                """
+        };
+        var output = TestHarness.RunModules(files, "main.ts", mode);
+        Assert.Equal("10\n15\n1\n3\n", output);
+    }
+}