diff --git a/ExpressionCompiler.cpp b/ExpressionCompiler.cpp
index 775d59a37..b90032daa 100644
--- a/ExpressionCompiler.cpp
+++ b/ExpressionCompiler.cpp
@@ -810,9 +810,9 @@ void ExpressionCompiler::LValue::setToZero(Expression const& _expression) const
 		if (stackDiff > 16)
 			BOOST_THROW_EXCEPTION(CompilerError() << errinfo_sourceLocation(_expression.getLocation())
 												  << errinfo_comment("Stack too deep."));
-		solAssert(stackDiff <= m_size, "");
+		solAssert(stackDiff >= m_size - 1, "");
 		for (unsigned i = 0; i < m_size; ++i)
-			*m_context << u256(0) << eth::swapInstruction(stackDiff + (m_size - i) )
+			*m_context << u256(0) << eth::swapInstruction(stackDiff + 1 - i)
 						<< eth::Instruction::POP;
 		break;
 	}