diff --git a/src/main/java/de/dogfire/dqfl/model/GridSize.java b/src/main/java/de/dogfire/dqfl/model/GridSize.java
index 02a49f2..ed172a9 100644
--- a/src/main/java/de/dogfire/dqfl/model/GridSize.java
+++ b/src/main/java/de/dogfire/dqfl/model/GridSize.java
@@ -60,6 +60,10 @@ public final class GridSize
 		{
 			final int rows = Integer.parseInt(parts[0].trim());
 			final int cols = Integer.parseInt(parts[1].trim());
+			if(rows <= 0 || cols <= 0)
+			{
+				return null;
+			}
 			return new GridSize(rows, cols);
 		}
 		catch(final NumberFormatException e)