diff --git a/symbols/mdb/Mono.CompilerServices.SymbolWriter/MonoSymbolFile.cs b/symbols/mdb/Mono.CompilerServices.SymbolWriter/MonoSymbolFile.cs
index 937b0a516..6ad39d237 100644
--- a/symbols/mdb/Mono.CompilerServices.SymbolWriter/MonoSymbolFile.cs
+++ b/symbols/mdb/Mono.CompilerServices.SymbolWriter/MonoSymbolFile.cs
@@ -446,6 +446,11 @@ void CheckGuidMatch (Guid other, string filename, string assembly)
 		protected MonoSymbolFile (string filename, Mono.Cecil.ModuleDefinition module)
 			: this (filename)
 		{
+			// Check that the MDB file matches the module, if we have been
+			// passed a module.
+			if (module == null)
+				return;
+
 			CheckGuidMatch (module.Mvid, filename, module.FullyQualifiedName);
 		}
 
@@ -485,7 +490,7 @@ public static MonoSymbolFile ReadSymbolFile (Assembly assembly)
 
 		public static MonoSymbolFile ReadSymbolFile (string mdbFilename)
 		{
-			return new MonoSymbolFile (mdbFilename, null);
+			return new MonoSymbolFile (mdbFilename);
 		}
 
 		public int CompileUnitCount {