diff --git a/src/writer/msl/generator_impl.cc b/src/writer/msl/generator_impl.cc
index 0a2c72f..70b78fe 100644
--- a/src/writer/msl/generator_impl.cc
+++ b/src/writer/msl/generator_impl.cc
@@ -386,7 +386,7 @@
     return EmitUnaryOp(expr->AsUnaryOp());
   }
 
-  error_ = "unknown expression type";
+  error_ = "unknown expression type: " + expr->str();
   return false;
 }
 
@@ -648,7 +648,7 @@
     return EmitSwitch(stmt->AsSwitch());
   }
 
-  error_ = "unknown statement type";
+  error_ = "unknown statement type: " + stmt->str();
   return false;
 }