diff --git a/llvm_emulator/stepper.py b/llvm_emulator/stepper.py
index aeb641d..8a89db1 100644
--- a/llvm_emulator/stepper.py
+++ b/llvm_emulator/stepper.py
@@ -486,7 +486,7 @@ def base_ty2size(base_ty):
     elif isinstance(base_ty, ll.PointerType):
         return 1
     elif isinstance(base_ty, ll.StructType):
-        return sum(map(base_ty2size, base_ty.fields))
+        return max(1, sum(map(base_ty2size, base_ty.fields)))
     else:
         # TODO
         err('base_ty2size: Unknown type or illegal type: {}'