diff --git a/toolchain/semantics/semantics_builtin_kind.cpp b/toolchain/semantics/semantics_builtin_kind.cpp
index 4828912684fd..100015b7359e 100644
--- a/toolchain/semantics/semantics_builtin_kind.cpp
+++ b/toolchain/semantics/semantics_builtin_kind.cpp
@@ -7,7 +7,8 @@
 namespace Carbon {
 
 CARBON_DEFINE_ENUM_CLASS_NAMES(SemanticsBuiltinKind) = {
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name) CARBON_ENUM_CLASS_NAME_STRING(Name)
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name) \
+  CARBON_ENUM_CLASS_NAME_STRING(Name)
 #include "toolchain/semantics/semantics_builtin_kind.def"
 };
 
diff --git a/toolchain/semantics/semantics_builtin_kind.def b/toolchain/semantics/semantics_builtin_kind.def
index e45848ddd885..ebe0c9c96e49 100644
--- a/toolchain/semantics/semantics_builtin_kind.def
+++ b/toolchain/semantics/semantics_builtin_kind.def
@@ -6,30 +6,56 @@
 //
 // It does not use `#include` guards, and instead is designed to be `#include`ed
 // after the x-macro is defined in order for its inclusion to expand to the
-// desired output. The x-macro for this header is `CARBON_PARSE_NODE_KIND`. The
-// definition provided will be removed at the end of this file to clean up.
+// desired output.
+//
+// x-macros come in two forms:
+//   CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name)
+//     Used as a fallback if other macros are missing.
+//   CARBON_SEMANTICS_BUILTIN_KIND(Name, Type)
+//     Defines a builtin kind with the associated type, which must also be
+//     builtin.
+//
+// Note that Invalid is provided with CARBON_SEMANTICS_BUILTIN_KIND_NAME but not
+// CARBON_SEMANTICS_BUILTIN_KIND.
 
+#if !(defined(CARBON_SEMANTICS_BUILTIN_KIND_NAME) || \
+      defined(CARBON_SEMANTICS_BUILTIN_KIND))
+#error \
+    "Must define CARBON_SEMANTICS_BUILTIN_KIND family x-macros to use this file."
+#endif
+
+// If CARBON_SEMANTICS_BUILTIN_KIND_NAME is undefined, ignore calls.
+#ifndef CARBON_SEMANTICS_BUILTIN_KIND_NAME
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name)
+#endif
+
+// If CARBON_SEMANTICS_BUILTIN_KIND is undefined, delegate calls to
+// CARBON_SEMANTICS_BUILTIN_KIND_NAME.
 #ifndef CARBON_SEMANTICS_BUILTIN_KIND
-#error "Must define the x-macro to use this file."
+#define CARBON_SEMANTICS_BUILTIN_KIND(Name, ...) \
+  CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name)
 #endif
 
 // Tracks expressions which are valid as types.
-CARBON_SEMANTICS_BUILTIN_KIND(TypeType)
+// This has a deliberately self-referential type.
+CARBON_SEMANTICS_BUILTIN_KIND(TypeType, TypeType)
 
 // Used when a SemanticNode has an invalid type, which should then be ignored
 // for future type checking.
-CARBON_SEMANTICS_BUILTIN_KIND(InvalidType)
+// This has a deliberately self-referential type.
+CARBON_SEMANTICS_BUILTIN_KIND(InvalidType, InvalidType)
 
 // The type of integers and integer literals, currently always i32. Long-term
 // we may not want it this way, but for now this is the approach.
-CARBON_SEMANTICS_BUILTIN_KIND(IntegerType)
+CARBON_SEMANTICS_BUILTIN_KIND(IntegerType, TypeType)
 
 // The type of reals and real literals, currently always f64. Long-term
 // we may not want it this way, but for now this is the approach.
-CARBON_SEMANTICS_BUILTIN_KIND(RealType)
+CARBON_SEMANTICS_BUILTIN_KIND(RealType, TypeType)
 
 // Keep invalid last, so that we can use values as array indices without needing
 // an invalid entry.
-CARBON_SEMANTICS_BUILTIN_KIND(Invalid)
+CARBON_SEMANTICS_BUILTIN_KIND_NAME(Invalid)
 
+#undef CARBON_SEMANTICS_BUILTIN_KIND_NAME
 #undef CARBON_SEMANTICS_BUILTIN_KIND
diff --git a/toolchain/semantics/semantics_builtin_kind.h b/toolchain/semantics/semantics_builtin_kind.h
index c48287736a1f..53a9d919c64b 100644
--- a/toolchain/semantics/semantics_builtin_kind.h
+++ b/toolchain/semantics/semantics_builtin_kind.h
@@ -12,13 +12,14 @@
 namespace Carbon {
 
 CARBON_DEFINE_RAW_ENUM_CLASS(SemanticsBuiltinKind, uint8_t) {
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name) CARBON_RAW_ENUM_ENUMERATOR(Name)
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name) \
+  CARBON_RAW_ENUM_ENUMERATOR(Name)
 #include "toolchain/semantics/semantics_builtin_kind.def"
 };
 
 class SemanticsBuiltinKind : public CARBON_ENUM_BASE(SemanticsBuiltinKind) {
  public:
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name) \
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name) \
   CARBON_ENUM_CONSTANT_DECLARATION(Name)
 #include "toolchain/semantics/semantics_builtin_kind.def"
 
@@ -34,7 +35,7 @@ class SemanticsBuiltinKind : public CARBON_ENUM_BASE(SemanticsBuiltinKind) {
   using EnumBase::FromInt;
 };
 
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name) \
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name) \
   CARBON_ENUM_CONSTANT_DEFINITION(SemanticsBuiltinKind, Name)
 #include "toolchain/semantics/semantics_builtin_kind.def"
 
diff --git a/toolchain/semantics/semantics_ir.cpp b/toolchain/semantics/semantics_ir.cpp
index c99d95880a1a..3485de59e5d7 100644
--- a/toolchain/semantics/semantics_ir.cpp
+++ b/toolchain/semantics/semantics_ir.cpp
@@ -14,33 +14,19 @@ namespace Carbon {
 
 auto SemanticsIR::MakeBuiltinIR() -> SemanticsIR {
   SemanticsIR semantics(/*builtin_ir=*/nullptr);
-  auto block_id = semantics.AddNodeBlock();
   semantics.nodes_.reserve(SemanticsBuiltinKind::ValidCount);
 
-  constexpr int32_t TypeOfTypeType = 0;
-  auto type_type = semantics.AddNode(
-      block_id, SemanticsNode::MakeBuiltin(SemanticsBuiltinKind::TypeType,
-                                           SemanticsNodeId(TypeOfTypeType)));
-  CARBON_CHECK(type_type.index == TypeOfTypeType)
-      << "TypeType's type must be self-referential.";
+#define CARBON_SEMANTICS_BUILTIN_KIND(Name, Type)        \
+  semantics.nodes_.push_back(SemanticsNode::MakeBuiltin( \
+      SemanticsBuiltinKind::Name, SemanticsNodeId::Builtin##Type));
+#include "toolchain/semantics/semantics_builtin_kind.def"
 
-  constexpr int32_t TypeOfInvalidType = 1;
-  auto invalid_type = semantics.AddNode(
-      block_id, SemanticsNode::MakeBuiltin(SemanticsBuiltinKind::InvalidType,
-                                           SemanticsNodeId(TypeOfInvalidType)));
-  CARBON_CHECK(invalid_type.index == TypeOfInvalidType)
-      << "InvalidType's type must be self-referential.";
-
-  semantics.AddNode(
-      block_id,
-      SemanticsNode::MakeBuiltin(SemanticsBuiltinKind::IntegerType, type_type));
-
-  semantics.AddNode(block_id, SemanticsNode::MakeBuiltin(
-                                  SemanticsBuiltinKind::RealType, type_type));
-
-  CARBON_CHECK(semantics.node_blocks_.size() == 2)
-      << "BuildBuiltins should produce 2 blocks, actual: "
+  CARBON_CHECK(semantics.node_blocks_.size() == 1)
+      << "BuildBuiltins should only have the empty block, actual: "
       << semantics.node_blocks_.size();
+  CARBON_CHECK(semantics.nodes_.size() == SemanticsBuiltinKind::ValidCount)
+      << "BuildBuiltins should produce " << SemanticsBuiltinKind::ValidCount
+      << " nodes, actual: " << semantics.nodes_.size();
   return semantics;
 }
 
diff --git a/toolchain/semantics/semantics_node.h b/toolchain/semantics/semantics_node.h
index a366985e5b99..1e8fdf0721cf 100644
--- a/toolchain/semantics/semantics_node.h
+++ b/toolchain/semantics/semantics_node.h
@@ -22,7 +22,7 @@ struct SemanticsNodeId : public IndexBase {
   static const SemanticsNodeId Invalid;
 
 // Builtin node IDs.
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name) \
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name) \
   static const SemanticsNodeId Builtin##Name;
 #include "toolchain/semantics/semantics_builtin_kind.def"
 
@@ -37,7 +37,7 @@ constexpr SemanticsNodeId SemanticsNodeId::Invalid = SemanticsNodeId();
 
 // Uses the cross-reference node ID for a builtin. This relies on SemanticsIR
 // guarantees for builtin cross-reference placement.
-#define CARBON_SEMANTICS_BUILTIN_KIND(Name)                  \
+#define CARBON_SEMANTICS_BUILTIN_KIND_NAME(Name)             \
   constexpr SemanticsNodeId SemanticsNodeId::Builtin##Name = \
       SemanticsNodeId(SemanticsBuiltinKind::Name.AsInt());
 #include "toolchain/semantics/semantics_builtin_kind.def"