diff --git a/userspace/engine/falco_source.h b/userspace/engine/falco_source.h
index d443b2ba..b222054e 100644
--- a/userspace/engine/falco_source.h
+++ b/userspace/engine/falco_source.h
@@ -56,12 +56,30 @@ struct falco_source
 	// matches an event.
 	mutable std::vector<falco_rule> m_rules;
 
-	inline bool is_field_defined(const std::string& field) const
+	inline bool is_valid_lhs_field(const std::string& field) const
 	{
-		if (filter_factory->new_filtercheck(field.c_str()) != nullptr)
+		// if there's at least one parenthesis we may be parsing a field
+		// wrapped inside one or more transformers. In those cases, the most
+		// rigorous analysis we can do is compiling a simple filter using
+		// the field as left-hand side of a comparison, and see if any error
+		// occurs.
+		if (field.find('(') != std::string::npos)
 		{
-			return true;
+			try
+			{
+				auto filter = field;
+				filter.append(" exists");
+				sinsp_filter_compiler(filter_factory, filter).compile();
+				return true;
+			}
+			catch (...)
+			{
+				return false;
+			}
 		}
-		return false;
+
+		// otherwise, simply attempt creating a filtercheck with the given
+		// field name and see if we succeed
+		return filter_factory->new_filtercheck(field.c_str()) != nullptr;
 	}
 };
diff --git a/userspace/engine/rule_loader_collector.cpp b/userspace/engine/rule_loader_collector.cpp
index 1832e1b6..394e8a79 100644
--- a/userspace/engine/rule_loader_collector.cpp
+++ b/userspace/engine/rule_loader_collector.cpp
@@ -88,7 +88,7 @@ static void validate_exception_info(
 		{
 			for (const auto &v : ex.fields.items)
 			{
-				THROW(!source->is_field_defined(v.item),
+				THROW(!source->is_valid_lhs_field(v.item),
 					std::string("'") + v.item + "' is not a supported filter field",
 					ex.ctx);
 			}
@@ -109,7 +109,7 @@ static void validate_exception_info(
 		      ex.ctx);
 		if (source)
 		{
-			THROW(!source->is_field_defined(ex.fields.item),
+			THROW(!source->is_valid_lhs_field(ex.fields.item),
 				std::string("'") + ex.fields.item + "' is not a supported filter field",
 				ex.ctx);
 		}