diff --git a/Assets/UXF/Scripts/Session.cs b/Assets/UXF/Scripts/Session.cs
index 23f66c9a..47e4ddff 100644
--- a/Assets/UXF/Scripts/Session.cs
+++ b/Assets/UXF/Scripts/Session.cs
@@ -618,9 +618,25 @@ Trial GetPrevTrial()
         /// </summary>
         /// <returns></returns>
         Trial GetFirstTrial()
-        {
-            var firstBlock = blocks[0];
-            return firstBlock.trials[0];
+        {   
+            Block firstBlock;
+            try
+            {
+                firstBlock = blocks[0];
+            }
+            catch (ArgumentOutOfRangeException)
+            {
+                throw new NoSuchTrialException("There is no first trial because no blocks have been created!");
+            }
+
+            try
+            {
+                return firstBlock.trials[0];
+            }
+            catch (ArgumentOutOfRangeException)
+            {
+                throw new NoSuchTrialException("There is no first trial. No trials exist in the first block.");
+            }
         }
 
         /// <summary>
@@ -629,8 +645,24 @@ Trial GetFirstTrial()
         /// <returns></returns>
         Trial GetLastTrial()
         {
-            var lastBlock = blocks[blocks.Count - 1];
-            return lastBlock.trials[lastBlock.trials.Count - 1];
+            Block lastBlock;
+            try
+            {
+                lastBlock = blocks[0];
+            }
+            catch (ArgumentOutOfRangeException)
+            {
+                throw new NoSuchTrialException("There is no last trial because no blocks have been created!");
+            }
+            
+            try
+            {
+                return lastBlock.trials[lastBlock.trials.Count - 1];
+            }
+            catch (ArgumentOutOfRangeException)
+            {
+                throw new NoSuchTrialException("There is no last trial. No trials exist in the last block.");
+            }
         }
 
         /// <summary>
diff --git a/Assets/UXF/Scripts/Tests/Editor/TestSessionBuilding.cs b/Assets/UXF/Scripts/Tests/Editor/TestSessionBuilding.cs
index 2b736a45..239f3a91 100644
--- a/Assets/UXF/Scripts/Tests/Editor/TestSessionBuilding.cs
+++ b/Assets/UXF/Scripts/Tests/Editor/TestSessionBuilding.cs
@@ -129,6 +129,35 @@ public void SwapTrials()
             session.blocks = new List<Block>();
 
 		}
+
+		[Test]
+		public void InvalidTrialAccess()
+		{
+			Block block = session.CreateBlock();
+
+			Assert.Throws<NoSuchTrialException>(
+				delegate { Trial t = session.FirstTrial; }
+			);
+
+			Assert.Throws<NoSuchTrialException>(
+				delegate { Trial t = session.LastTrial; }
+			);
+
+			// reset blocks
+            session.blocks = new List<Block>();
+		}
+
+		[Test]
+		public void InvalidBlockAccess()
+		{
+			Assert.Throws<NoSuchTrialException>(
+				delegate { Trial t = session.FirstTrial; }
+			);
+
+			Assert.Throws<NoSuchTrialException>(
+				delegate { Trial t = session.LastTrial; }
+			);
+		}
 		
 	}