diff --git a/crates/csharp/src/interface.rs b/crates/csharp/src/interface.rs
index 849df02b1..2c0df7736 100644
--- a/crates/csharp/src/interface.rs
+++ b/crates/csharp/src/interface.rs
@@ -537,12 +537,14 @@ impl InterfaceGenerator<'_> {
         };
 
         let access = self.csharp_gen.access_modifier();
+        let qualifier = self.csharp_gen.qualifier();
 
         uwrite!(
             self.csharp_interop_src,
             r#"
             [global::System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute(EntryPoint = "{export_name}")]
             {access} static unsafe {wasm_result_type} {interop_name}({wasm_params}) {{
+                {qualifier}WasmInteropInitializer.EnsureInitialized();
                 {vars}
                 {src}
             }}
diff --git a/crates/csharp/src/world_generator.rs b/crates/csharp/src/world_generator.rs
index b58bbb026..f56fe4051 100644
--- a/crates/csharp/src/world_generator.rs
+++ b/crates/csharp/src/world_generator.rs
@@ -41,6 +41,7 @@ pub struct CSharp {
     pub(crate) all_resources: HashMap<TypeId, ResourceInfo>,
     pub(crate) world_resources: HashMap<TypeId, ResourceInfo>,
     pub(crate) import_funcs_called: bool,
+    pub(crate) has_exports: bool,
 }
 
 impl CSharp {
@@ -182,6 +183,7 @@ impl WorldGenerator for CSharp {
         id: InterfaceId,
         _files: &mut Files,
     ) -> anyhow::Result<()> {
+        self.has_exports = true;
         let name = interface_name(self, resolve, key, Direction::Export);
         self.interface_names.insert(id, name.clone());
         let mut r#gen = self.interface(resolve, &name, Direction::Export);
@@ -226,6 +228,7 @@ impl WorldGenerator for CSharp {
         funcs: &[(&str, &Function)],
         _files: &mut Files,
     ) -> anyhow::Result<()> {
+        self.has_exports = true;
         let name = &format!("{}-world", resolve.worlds[world].name).to_upper_camel_case();
         let name = &format!("{name}.I{name}");
         let mut r#gen = self.interface(resolve, name, Direction::Export);
@@ -491,6 +494,39 @@ impl WorldGenerator for CSharp {
             src.push_str(include_str!("RepTable.cs"));
         }
 
+        // Add initialization guard for reactor (library) components.
+        // In reactor mode, there's no _start entry point, so exports may be called
+        // before the .NET runtime is fully initialized. This guard ensures that
+        // the runtime initialization (via __wasm_call_ctors) runs before any
+        // exported function executes.
+        // See: https://github.com/bytecodealliance/componentize-dotnet/issues/103
+        if self.has_exports {
+            uwrite!(
+                src,
+                r#"
+                internal static class WasmInteropInitializer
+                {{
+                    private static volatile bool _initialized;
+                    private static readonly object _lock = new object();
+
+                    [global::System.Runtime.InteropServices.DllImportAttribute("*", EntryPoint = "__wasm_call_ctors")]
+                    private static extern void WasmCallCtors();
+
+                    internal static void EnsureInitialized()
+                    {{
+                        if (_initialized) return;
+                        lock (_lock)
+                        {{
+                            if (_initialized) return;
+                            WasmCallCtors();
+                            _initialized = true;
+                        }}
+                    }}
+                }}
+                "#
+            );
+        }
+
         if !&self.world_fragments.is_empty() {
             src.push_str("\n");