diff --git a/lib/fizzy/execute.cpp b/lib/fizzy/execute.cpp
index 2960268df..a1789bd69 100644
--- a/lib/fizzy/execute.cpp
+++ b/lib/fizzy/execute.cpp
@@ -465,12 +465,11 @@ inline bool invoke_function(const FuncType& func_type, uint32_t func_idx, Instan
 
     stack.drop(num_args);
 
-    const auto num_outputs = func_type.outputs.size();
     // NOTE: we can assume these two from validation
-    assert(num_outputs <= 1);
-    assert(ret.has_value == (num_outputs == 1));
+    assert(func_type.outputs.size() <= 1);
+    assert(ret.has_value == !func_type.outputs.empty());
     // Push back the result
-    if (num_outputs != 0)
+    if (ret.has_value != 0)
         stack.push(ret.value);
 
     return true;