diff --git a/src/wren/vm.cpp b/src/wren/vm.cpp
index d0d01b7..3acd89a 100644
--- a/src/wren/vm.cpp
+++ b/src/wren/vm.cpp
@@ -67,10 +67,15 @@ namespace wren {
 			assert(cb);
 			assert(cb->foreign_method_fn and cb->config_obj and cb->owner);
 			foreign_method_t func = cb->foreign_method_fn(*cb->config_obj, cb->owner, module, class_name, is_static, signature);
-			DynafuncMaker* const dfm = cb->dynafunc;
-			assert(dfm);
-			auto retval = reinterpret_cast<WrenForeignMethodFn>(dfm->make(cb->owner, func));
-			return retval;
+			if (func) {
+				DynafuncMaker* const dfm = cb->dynafunc;
+				assert(dfm);
+				auto retval = reinterpret_cast<WrenForeignMethodFn>(dfm->make(cb->owner, func));
+				return retval;
+			}
+			else {
+				return nullptr;
+			}
 		}
 
 		WrenForeignClassMethods foreign_class_fn (WrenVM* wvm, const char* module, const char* class_name) {
@@ -78,10 +83,15 @@ namespace wren {
 			assert(cb);
 			assert(cb->foreign_class_fn and cb->config_obj and cb->owner);
 			foreign_class_t funcs = cb->foreign_class_fn(*cb->config_obj, cb->owner, module, class_name);
-			DynafuncMaker* const dfm = cb->dynafunc;
-			assert(dfm);
 			WrenForeignClassMethods retval;
-			retval.allocate = reinterpret_cast<WrenForeignMethodFn>(dfm->make(cb->owner, funcs.allocate));
+			if (funcs.allocate) {
+				DynafuncMaker* const dfm = cb->dynafunc;
+				assert(dfm);
+				retval.allocate = reinterpret_cast<WrenForeignMethodFn>(dfm->make(cb->owner, funcs.allocate));
+			}
+			else {
+				retval.allocate = nullptr;
+			}
 			retval.finalize = funcs.finalize;
 			return retval;
 		}