Index: src/AST/Convert.cpp
===================================================================
--- src/AST/Convert.cpp	(revision 798a8b33d41aef379aeeb2830e27a51928291097)
+++ src/AST/Convert.cpp	(revision 8110bc3a1ba874ee9362cfeb80aca91d34d22b54)
@@ -2415,4 +2415,15 @@
 	}
 
+	virtual void visit( const DimensionExpr * old ) override final {
+		// DimensionExpr gets desugared away in Validate.
+		// As long as new-AST passes don't use it, this cheap-cheerful error
+		// detection helps ensure that these occurrences have been compiled
+		// away, as expected.  To move the DimensionExpr boundary downstream
+		// or move the new-AST translation boundary upstream, implement
+		// DimensionExpr in the new AST and implement a conversion.
+		(void) old;
+		assert(false && "DimensionExpr should not be present at new-AST boundary");
+	}
+
 	virtual void visit( const AsmExpr * old ) override final {
 		this->node = visitBaseExpr( old,
Index: src/AST/Decl.cpp
===================================================================
--- src/AST/Decl.cpp	(revision 798a8b33d41aef379aeeb2830e27a51928291097)
+++ src/AST/Decl.cpp	(revision 8110bc3a1ba874ee9362cfeb80aca91d34d22b54)
@@ -78,5 +78,5 @@
 
 const char * TypeDecl::typeString() const {
-	static const char * kindNames[] = { "sized data type", "sized data type", "sized object type", "sized function type", "sized tuple type", "sized array length type" };
+	static const char * kindNames[] = { "sized data type", "sized data type", "sized object type", "sized function type", "sized tuple type", "sized length value" };
 	static_assert( sizeof(kindNames) / sizeof(kindNames[0]) == TypeDecl::NUMBER_OF_KINDS, "typeString: kindNames is out of sync." );
 	assertf( kind < TypeDecl::NUMBER_OF_KINDS, "TypeDecl kind is out of bounds." );
Index: src/AST/Decl.hpp
===================================================================
--- src/AST/Decl.hpp	(revision 798a8b33d41aef379aeeb2830e27a51928291097)
+++ src/AST/Decl.hpp	(revision 8110bc3a1ba874ee9362cfeb80aca91d34d22b54)
@@ -175,5 +175,5 @@
 class TypeDecl final : public NamedTypeDecl {
   public:
-	enum Kind { Dtype, DStype, Otype, Ftype, Ttype, ALtype, NUMBER_OF_KINDS };
+	enum Kind { Dtype, DStype, Otype, Ftype, Ttype, Dimension, NUMBER_OF_KINDS };
 
 	Kind kind;