diff --git a/BizHawk.MultiClient/tools/Watch/RamSearchEngine.cs b/BizHawk.MultiClient/tools/Watch/RamSearchEngine.cs
index f544a56410..e988d1c83f 100644
--- a/BizHawk.MultiClient/tools/Watch/RamSearchEngine.cs
+++ b/BizHawk.MultiClient/tools/Watch/RamSearchEngine.cs
@@ -200,7 +200,17 @@ namespace BizHawk.MultiClient
 		public Compare CompareTo
 		{
 			get { return _compareTo; }
-			set { _compareTo = value; } //TODO: check to see if this value is valid based on mode
+			set
+			{
+				if (CanDoCompareType(value))
+				{
+					_compareTo = value;
+				}
+				else
+				{
+					throw new InvalidOperationException();
+				}
+			}
 		}
 
 		public long? CompareValue
@@ -678,6 +688,18 @@ namespace BizHawk.MultiClient
 			}
 		}
 
+		private bool CanDoCompareType(Compare compareType)
+		{
+			switch (_settings.Mode)
+			{
+				default:
+				case Settings.SearchMode.Detailed:
+					return true;
+				case Settings.SearchMode.Fast:
+					return !(compareType == Compare.Changes);
+			}
+		}
+
 		#endregion
 
 		#region Classes