diff --git a/lib/runtime-c-api/wasmer.h b/lib/runtime-c-api/wasmer.h
index d5b628032..1e4941d36 100644
--- a/lib/runtime-c-api/wasmer.h
+++ b/lib/runtime-c-api/wasmer.h
@@ -215,7 +215,7 @@ wasmer_result_t wasmer_export_func_params_arity(const wasmer_export_func_t *func
  */
 wasmer_result_t wasmer_export_func_returns(const wasmer_export_func_t *func,
                                            wasmer_value_tag *returns,
-                                           int returns_len);
+                                           uint32_t returns_len);
 
 /**
  * Sets the result parameter to the arity of the returns of the wasmer_export_func_t
diff --git a/lib/runtime-c-api/wasmer.hh b/lib/runtime-c-api/wasmer.hh
index 8293ab2e7..12b5b0c70 100644
--- a/lib/runtime-c-api/wasmer.hh
+++ b/lib/runtime-c-api/wasmer.hh
@@ -192,7 +192,7 @@ wasmer_result_t wasmer_export_func_params_arity(const wasmer_export_func_t *func
 /// and `wasmer_last_error_message` to get an error message.
 wasmer_result_t wasmer_export_func_returns(const wasmer_export_func_t *func,
                                            wasmer_value_tag *returns,
-                                           int returns_len);
+                                           uint32_t returns_len);
 
 /// Sets the result parameter to the arity of the returns of the wasmer_export_func_t
 /// Returns `wasmer_result_t::WASMER_OK` upon success.