diff --git a/include/proxy-wasm/wasm.h b/include/proxy-wasm/wasm.h
index 9caf90173..e77b9b03d 100644
--- a/include/proxy-wasm/wasm.h
+++ b/include/proxy-wasm/wasm.h
@@ -196,10 +196,10 @@ class WasmBase : public std::enable_shared_from_this<WasmBase> {
   std::unordered_map<std::string, std::string>
       envs_; // environment variables passed through wasi.environ_get
 
-  WasmCallVoid<0> _initialize_; /* Emscripten v1.39.17+ */
-  WasmCallVoid<0> _start_;      /* Emscripten v1.39.0+ */
-  WasmCallVoid<0> __wasm_call_ctors_;
+  WasmCallVoid<0> _initialize_; /* WASI reactor (Emscripten v1.39.17+, Rust nightly) */
+  WasmCallVoid<0> _start_;      /* WASI command (Emscripten v1.39.0+, TinyGo) */
 
+  WasmCallWord<2> main_;
   WasmCallWord<1> malloc_;
 
   // Calls into the VM.
diff --git a/src/null/null_plugin.cc b/src/null/null_plugin.cc
index dfc2dbfaa..25f575e19 100644
--- a/src/null/null_plugin.cc
+++ b/src/null/null_plugin.cc
@@ -37,8 +37,6 @@ void NullPlugin::getFunction(std::string_view function_name, WasmCallVoid<0> *f)
     *f = nullptr;
   } else if (function_name == "_start") {
     *f = nullptr;
-  } else if (function_name == "__wasm_call_ctors") {
-    *f = nullptr;
   } else if (!wasm_vm_->integration()->getNullVmFunction(function_name, false, 0, this, f)) {
     error("Missing getFunction for: " + std::string(function_name));
     *f = nullptr;
@@ -167,7 +165,9 @@ void NullPlugin::getFunction(std::string_view function_name, WasmCallWord<1> *f)
 
 void NullPlugin::getFunction(std::string_view function_name, WasmCallWord<2> *f) {
   auto plugin = this;
-  if (function_name == "proxy_on_vm_start") {
+  if (function_name == "main") {
+    *f = nullptr;
+  } else if (function_name == "proxy_on_vm_start") {
     *f = [plugin](ContextBase *context, Word context_id, Word configuration_size) {
       SaveRestoreContext saved_context(context);
       return Word(plugin->onStart(context_id, configuration_size));
diff --git a/src/wasm.cc b/src/wasm.cc
index 2a6117ff0..7fda02629 100644
--- a/src/wasm.cc
+++ b/src/wasm.cc
@@ -147,8 +147,11 @@ void WasmBase::getFunctions() {
 #define _GET(_fn) wasm_vm_->getFunction(#_fn, &_fn##_);
 #define _GET_ALIAS(_fn, _alias) wasm_vm_->getFunction(#_alias, &_fn##_);
   _GET(_initialize);
-  _GET(_start);
-  _GET(__wasm_call_ctors);
+  if (_initialize_) {
+    _GET(main);
+  } else {
+    _GET(_start);
+  }
 
   _GET(malloc);
   if (!malloc_) {
@@ -284,11 +287,19 @@ ContextBase *WasmBase::getRootContext(const std::shared_ptr<PluginBase> &plugin,
 
 void WasmBase::startVm(ContextBase *root_context) {
   if (_initialize_) {
+    // WASI reactor.
     _initialize_(root_context);
+    if (main_) {
+      // Call main() if it exists in WASI reactor, to allow module to
+      // do early initialization (e.g. configure SDK).
+      //
+      // Re-using main() keeps this consistent when switching between
+      // WASI command (that calls main()) and reactor (that doesn't).
+      main_(root_context, Word(0), Word(0));
+    }
   } else if (_start_) {
+    // WASI command.
     _start_(root_context);
-  } else if (__wasm_call_ctors_) {
-    __wasm_call_ctors_(root_context);
   }
 }