diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -3229,10 +3229,10 @@
                    actual = ActualArgument(label.v);
                  },
                  [&](const parser::ActualArg::PercentRef &) {
-                   context_.Say("TODO: %REF() argument"_err_en_US);
+                   context_.Say("not yet implemented: %REF() intrinsic for arguments"_err_en_US);
                  },
                  [&](const parser::ActualArg::PercentVal &) {
-                   context_.Say("TODO: %VAL() argument"_err_en_US);
+                   context_.Say("not yet implemetned: %VAL() intrinsic for arguments"_err_en_US);
                  },
              },
       std::get<parser::ActualArg>(arg.t).u);
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -4721,7 +4721,7 @@
 }
 
 bool DeclarationVisitor::Pre(const parser::Union::UnionStmt &) {
-  Say("UNION is not yet supported"_err_en_US); // TODO
+  Say("not yet implemented: support for UNION"_err_en_US); // TODO
   return true;
 }
 
diff --git a/flang/runtime/edit-output.cpp b/flang/runtime/edit-output.cpp
--- a/flang/runtime/edit-output.cpp
+++ b/flang/runtime/edit-output.cpp
@@ -411,7 +411,7 @@
 template <int binaryPrecision>
 bool RealOutputEditing<binaryPrecision>::EditEXOutput(const DataEdit &) {
   io_.GetIoErrorHandler().Crash(
-      "EX output editing is not yet implemented"); // TODO
+      "not yet implemented: EX output editing"); // TODO
 }
 
 template <int KIND> bool RealOutputEditing<KIND>::Edit(const DataEdit &edit) {
diff --git a/flang/test/Semantics/struct01.f90 b/flang/test/Semantics/struct01.f90
--- a/flang/test/Semantics/struct01.f90
+++ b/flang/test/Semantics/struct01.f90
@@ -6,7 +6,7 @@
   structure /s/
     !ERROR: /s/ is not a known STRUCTURE
     record /s/ attemptToRecurse
-    !ERROR: UNION is not yet supported
+    !ERROR: not yet implemented: support for UNION
     union
       map
         integer j