diff --git a/DATabase/MergeDiff.cs b/DATabase/MergeDiff.cs
index 36762ed7..dab2e2fe 100644
--- a/DATabase/MergeDiff.cs
+++ b/DATabase/MergeDiff.cs
@@ -117,6 +117,7 @@ namespace SabreTools
 				ForcePacking = (_forceunpack ? ForcePacking.Unzip : ForcePacking.None),
 				OutputFormat = (_old ? OutputFormat.ClrMamePro : OutputFormat.Xml),
 				MergeRoms = _dedup,
+				Roms = new Dictionary<string, List<RomData>>(),
 				Type = (_superdat ? "SuperDAT" : ""),
 			};
 			foreach (string input in _inputs)
@@ -144,6 +145,7 @@ namespace SabreTools
 					ForcePacking = (_forceunpack ? ForcePacking.Unzip : ForcePacking.None),
 					OutputFormat = (_old ? OutputFormat.ClrMamePro : OutputFormat.Xml),
 					MergeRoms = _dedup,
+					Roms = new Dictionary<string, List<RomData>>(),
 				};
 				foreach (string key in userData.Roms.Keys)
 				{
@@ -187,6 +189,7 @@ namespace SabreTools
 						ForcePacking = (_forceunpack ? ForcePacking.Unzip : ForcePacking.None),
 						OutputFormat = (_old ? OutputFormat.ClrMamePro : OutputFormat.Xml),
 						MergeRoms = _dedup,
+						Roms = new Dictionary<string, List<RomData>>(),
 					};
 
 					foreach (string key in outerDiffData.Roms.Keys)
@@ -225,6 +228,7 @@ namespace SabreTools
 					ForcePacking = (_forceunpack ? ForcePacking.Unzip : ForcePacking.None),
 					OutputFormat = (_old ? OutputFormat.ClrMamePro : OutputFormat.Xml),
 					MergeRoms = _dedup,
+					Roms = new Dictionary<string, List<RomData>>(),
 				};
 				foreach (string key in userData.Roms.Keys)
 				{
@@ -269,6 +273,7 @@ namespace SabreTools
 						ForcePacking = (_forceunpack ? ForcePacking.Unzip : ForcePacking.None),
 						OutputFormat = (_old ? OutputFormat.ClrMamePro : OutputFormat.Xml),
 						MergeRoms = _dedup,
+						Roms = new Dictionary<string, List<RomData>>(),
 					};
 
 					List<string> keys = userData.Roms.Keys.ToList();