diff --git a/toolchain/check/custom_witness.cpp b/toolchain/check/custom_witness.cpp
index 704fc9798ac4..510a784c662a 100644
--- a/toolchain/check/custom_witness.cpp
+++ b/toolchain/check/custom_witness.cpp
@@ -551,45 +551,13 @@ auto BuildCustomWitness(Context& context, SemIR::LocId loc_id,
 }
 
 auto AsCoreIdentifier(SemIR::CoreInterface core_interface) -> CoreIdentifier {
-  using SemIR::CoreInterface;
   switch (core_interface) {
-    case CoreInterface::AddAssignWith:
-      return CoreIdentifier::AddAssignWith;
-    case CoreInterface::AddWith:
-      return CoreIdentifier::AddWith;
-    case CoreInterface::Copy:
-      return CoreIdentifier::Copy;
-    case CoreInterface::CppUnsafeDeref:
-      return CoreIdentifier::CppUnsafeDeref;
-    case CoreInterface::Dec:
-      return CoreIdentifier::Dec;
-    case CoreInterface::Default:
-      return CoreIdentifier::Default;
-    case CoreInterface::Destroy:
-      return CoreIdentifier::Destroy;
-    case CoreInterface::DivAssignWith:
-      return CoreIdentifier::DivAssignWith;
-    case CoreInterface::DivWith:
-      return CoreIdentifier::DivWith;
-    case CoreInterface::Inc:
-      return CoreIdentifier::Inc;
-    case CoreInterface::IntFitsIn:
-      return CoreIdentifier::IntFitsIn;
-    case CoreInterface::ModAssignWith:
-      return CoreIdentifier::ModAssignWith;
-    case CoreInterface::ModWith:
-      return CoreIdentifier::ModWith;
-    case CoreInterface::MulAssignWith:
-      return CoreIdentifier::MulAssignWith;
-    case CoreInterface::MulWith:
-      return CoreIdentifier::MulWith;
-    case CoreInterface::Negate:
-      return CoreIdentifier::Negate;
-    case CoreInterface::SubAssignWith:
-      return CoreIdentifier::SubAssignWith;
-    case CoreInterface::SubWith:
-      return CoreIdentifier::SubWith;
-    case CoreInterface::Unknown:
+#define CARBON_SEM_IR_CORE_INTERFACE_EXCLUDE_UNKNOWN
+#define CARBON_SEM_IR_CORE_INTERFACE_KIND(Name) \
+  case SemIR::CoreInterface::Name:              \
+    return CoreIdentifier::Name;
+#include "toolchain/sem_ir/core_interface_kind.def"
+    case SemIR::CoreInterface::Unknown:
       CARBON_FATAL("{0} doesn't have a `CoreIdentifier` mapping",
                    core_interface);
   }
diff --git a/toolchain/check/handle_interface.cpp b/toolchain/check/handle_interface.cpp
index 61311479e9f0..9345a5214800 100644
--- a/toolchain/check/handle_interface.cpp
+++ b/toolchain/check/handle_interface.cpp
@@ -91,26 +91,13 @@ static auto BuildInterfaceDecl(Context& context,
 
     if (context.sem_ir().package_id() == PackageNameId::Core) {
       auto name = context.names().GetIRBaseName(interface_info.name_id);
+      // This is awful for readability, but it's the only viable way to ensure
+      // adding new core interfaces are automatically picked up.
       interface_info.core_interface =
           llvm::StringSwitch<SemIR::CoreInterface>(name)
-              .Case("AddAssignWith", SemIR::CoreInterface::AddAssignWith)
-              .Case("AddWith", SemIR::CoreInterface::AddWith)
-              .Case("Copy", SemIR::CoreInterface::Copy)
-              .Case("CppUnsafeDeref", SemIR::CoreInterface::CppUnsafeDeref)
-              .Case("Dec", SemIR::CoreInterface::Dec)
-              .Case("Default", SemIR::CoreInterface::Default)
-              .Case("Destroy", SemIR::CoreInterface::Destroy)
-              .Case("DivAssignWith", SemIR::CoreInterface::DivAssignWith)
-              .Case("DivWith", SemIR::CoreInterface::DivWith)
-              .Case("Inc", SemIR::CoreInterface::Inc)
-              .Case("IntFitsIn", SemIR::CoreInterface::IntFitsIn)
-              .Case("ModAssignWith", SemIR::CoreInterface::ModAssignWith)
-              .Case("ModWith", SemIR::CoreInterface::ModWith)
-              .Case("MulAssignWith", SemIR::CoreInterface::MulAssignWith)
-              .Case("MulWith", SemIR::CoreInterface::MulWith)
-              .Case("Negate", SemIR::CoreInterface::Negate)
-              .Case("SubAssignWith", SemIR::CoreInterface::SubAssignWith)
-              .Case("SubWith", SemIR::CoreInterface::SubWith)
+#define CARBON_SEM_IR_CORE_INTERFACE_KIND(Name) \
+  .Case(#Name, SemIR::CoreInterface::Name)
+#include "toolchain/sem_ir/core_interface_kind.def"
               .Default(SemIR::CoreInterface::Unknown);
     }
     interface_decl.interface_id = context.interfaces().Add(interface_info);
diff --git a/toolchain/sem_ir/core_interface_kind.def b/toolchain/sem_ir/core_interface_kind.def
index bee6546beea8..098bed023697 100644
--- a/toolchain/sem_ir/core_interface_kind.def
+++ b/toolchain/sem_ir/core_interface_kind.def
@@ -35,6 +35,9 @@ CARBON_SEM_IR_CORE_INTERFACE_KIND(Negate)
 CARBON_SEM_IR_CORE_INTERFACE_KIND(SubAssignWith)
 CARBON_SEM_IR_CORE_INTERFACE_KIND(SubWith)
 
+#ifndef CARBON_SEM_IR_CORE_INTERFACE_EXCLUDE_UNKNOWN
 CARBON_SEM_IR_CORE_INTERFACE_KIND(Unknown)
+#endif  // CARBON_SEM_IR_CORE_INTERFACE_EXCLUDE_UNKNOWN
 
 #undef CARBON_SEM_IR_CORE_INTERFACE_KIND
+#undef CARBON_SEM_IR_CORE_INTERFACE_EXCLUDE_UNKNOWN