diff --git a/org.adempiere.ui.swing/src/org/compiere/grid/ed/Calculator.java b/org.adempiere.ui.swing/src/org/compiere/grid/ed/Calculator.java
index 588f6a1d63..8b10008888 100644
--- a/org.adempiere.ui.swing/src/org/compiere/grid/ed/Calculator.java
+++ b/org.adempiere.ui.swing/src/org/compiere/grid/ed/Calculator.java
@@ -367,7 +367,7 @@ public final class Calculator extends CDialog
 			case '/':		case '*':
 			case '-':       case '+':
 			case '%':
-				if (m_display.length() > 1)
+				if (m_display.length() > 0)
 				{
 					char last = m_display.charAt(m_display.length()-1);
 					if (OPERANDS.indexOf(last) == -1)