diff --git a/src/thingdef/thingdef_exp.h b/src/thingdef/thingdef_exp.h
index f81dd2b54..8901e35c3 100644
--- a/src/thingdef/thingdef_exp.h
+++ b/src/thingdef/thingdef_exp.h
@@ -195,6 +195,7 @@ protected:
 	{
 		isresolved = false;
 		ScriptPosition = pos;
+		ValueType = VAL_Unresolved;
 	}
 public:
 	virtual ~FxExpression() {}
diff --git a/src/thingdef/thingdef_type.h b/src/thingdef/thingdef_type.h
index 706b2ba7a..1707a8939 100644
--- a/src/thingdef/thingdef_type.h
+++ b/src/thingdef/thingdef_type.h
@@ -8,6 +8,7 @@
 
 enum ExpValType
 {
+	VAL_Unresolved,	// type not yet known
 	VAL_Int,		// integer number
 	VAL_Float,		// floating point number
 	VAL_Unknown,	// nothing