diff --git a/src/Riok.Mapperly/Descriptors/Mappings/DerivedExistingTargetTypeMapping.cs b/src/Riok.Mapperly/Descriptors/Mappings/DerivedExistingTargetTypeMapping.cs
index 041f902157..eb4f45b397 100644
--- a/src/Riok.Mapperly/Descriptors/Mappings/DerivedExistingTargetTypeMapping.cs
+++ b/src/Riok.Mapperly/Descriptors/Mappings/DerivedExistingTargetTypeMapping.cs
@@ -31,48 +31,49 @@ IReadOnlyCollection<IExistingTargetMapping> existingTargetTypeMappings
     public override IEnumerable<StatementSyntax> Build(TypeMappingBuildContext ctx, ExpressionSyntax target)
     {
         var sourceExpression = TupleExpression(CommaSeparatedList(Argument(ctx.Source), Argument(target)));
-        var sections = _existingTargetTypeMappings.Select(x => BuildSwitchSection(ctx, x)).Append(BuildDefaultSwitchSection(ctx));
+        var sections = _existingTargetTypeMappings.Select(x => BuildSwitchSection(ctx, x)).Append(BuildDefaultSwitchSection(ctx, target));
 
         yield return ctx.SyntaxFactory.SwitchStatement(sourceExpression, List(sections)).AddLeadingLineFeed(ctx.SyntaxFactory.Indentation);
     }
 
     private SwitchSectionSyntax BuildSwitchSection(TypeMappingBuildContext ctx, IExistingTargetMapping mapping)
     {
-        // MapToB(source, target);
         var (sectionCtx, sourceVariableName) = ctx.WithNewScopedSource(SourceName);
         var targetVariableName = sectionCtx.NameBuilder.New(TargetName);
         sectionCtx = sectionCtx.AddIndentation();
 
+        // (A source, B target)
         var positionalTypeMatch = PositionalPatternClause(
             CommaSeparatedList(
                 Subpattern(DeclarationPattern(mapping.SourceType, sourceVariableName)),
                 Subpattern(DeclarationPattern(mapping.TargetType, targetVariableName))
             )
         );
-
         var pattern = RecursivePattern().WithPositionalPatternClause(positionalTypeMatch);
-        var caseLabel = CasePatternSwitchLabel(pattern).AddLeadingLineFeed(sectionCtx.SyntaxFactory.Indentation);
 
-        var target = IdentifierName(targetVariableName);
+        // case (A source, B target):
+        var caseLabel = CasePatternSwitchLabel(pattern).AddLeadingLineFeed(sectionCtx.SyntaxFactory.Indentation);
 
         var statementContext = sectionCtx.AddIndentation();
-        var statements = List(
-            mapping.Build(statementContext, target).Append(BreakStatement().AddLeadingLineFeed(statementContext.SyntaxFactory.Indentation))
-        );
-        var section = SwitchSection().WithLabels(SingletonList<SwitchLabelSyntax>(caseLabel)).WithStatements(statements);
 
-        return section;
+        // break;
+        var breakStatement = BreakStatement().AddLeadingLineFeed(statementContext.SyntaxFactory.Indentation);
+        var target = IdentifierName(targetVariableName);
+        var statements = List(mapping.Build(statementContext, target).Append(breakStatement));
+
+        return SwitchSection().WithLabels(SingletonList<SwitchLabelSyntax>(caseLabel)).WithStatements(statements);
     }
 
-    private SwitchSectionSyntax BuildDefaultSwitchSection(TypeMappingBuildContext ctx)
+    private SwitchSectionSyntax BuildDefaultSwitchSection(TypeMappingBuildContext ctx, ExpressionSyntax target)
     {
         // default:
         var defaultCaseLabel = DefaultSwitchLabel().AddLeadingLineFeed(ctx.SyntaxFactory.Indentation + 1);
 
         // throw new ArgumentException(msg, nameof(ctx.Source)),
         var sourceType = Invocation(MemberAccess(ctx.Source, GetTypeMethodName));
+        var targetType = Invocation(MemberAccess(target, GetTypeMethodName));
         var throwExpression = ThrowArgumentExpression(
-                InterpolatedString($"Cannot map {sourceType} to {TargetType.ToDisplayString()} as there is no known derived type mapping"),
+                InterpolatedString($"Cannot map {sourceType} to {targetType} as there is no known derived type mapping"),
                 ctx.Source
             )
             .AddLeadingLineFeed(ctx.SyntaxFactory.Indentation + 2);