diff --git a/ecsact/wasm.h b/ecsact/wasm.h
index 0aa2d34..6ce7727 100644
--- a/ecsact/wasm.h
+++ b/ecsact/wasm.h
@@ -95,6 +95,12 @@ typedef enum ecsactsi_wasm_error {
 	 * Invoking `_initialize()` resulted in a wasm trap
 	 */
 	ECSACTSI_WASM_ERR_INITIALIZE_FAIL,
+
+	/**
+	 * Ecsact dynamic module is 'load at runtime' but
+	 * 'ecsact_set_system_execution_impl' has not been set.
+	 */
+	ECSACTSI_WASM_ERR_NO_SET_SYSTEM_EXECUTION,
 } ecsactsi_wasm_error;
 
 ECSACTSI_WASM_API_FN(void, ecsactsi_wasm_last_error_message)
diff --git a/ecsact/wasm/detail/wasm.cc b/ecsact/wasm/detail/wasm.cc
index c3de878..4e92342 100644
--- a/ecsact/wasm/detail/wasm.cc
+++ b/ecsact/wasm/detail/wasm.cc
@@ -121,6 +121,12 @@ ecsactsi_wasm_error ecsactsi_wasm_load(
 	using ecsact::wasm::detail::minst_error_code;
 	using ecsact::wasm::detail::minst_export;
 
+#ifdef ECSACT_DYNAMIC_API_LOAD_AT_RUNTIME
+	if(ecsact_set_system_execution_impl == nullptr) {
+		return ECSACTSI_WASM_ERR_NO_SET_SYSTEM_EXECUTION;
+	}
+#endif
+
 	auto result = ecsact::wasm::detail::minst::create(
 		engine(),
 		std::span{