diff --git a/explorer/interpreter/type_checker.cpp b/explorer/interpreter/type_checker.cpp
index 5e06209a968d..db0569bb714c 100644
--- a/explorer/interpreter/type_checker.cpp
+++ b/explorer/interpreter/type_checker.cpp
@@ -6168,7 +6168,6 @@ static auto IsValidTypeForAliasTarget(Nonnull<const Value*> type) -> bool {
     case Value::Kind::StructValue:
     case Value::Kind::NominalClassValue:
     case Value::Kind::MixinPseudoType:
-    case Value::Kind::TypeOfMixinPseudoType:
     case Value::Kind::AlternativeValue:
     case Value::Kind::TupleValue:
     case Value::Kind::ImplWitness:
@@ -6182,11 +6181,11 @@ static auto IsValidTypeForAliasTarget(Nonnull<const Value*> type) -> bool {
     case Value::Kind::AlternativeConstructorValue:
     case Value::Kind::StringValue:
     case Value::Kind::UninitializedValue:
-      CARBON_FATAL() << "type of alias target is not a type";
+      CARBON_FATAL() << "type of alias target is not a type: " << *type;
 
     case Value::Kind::AutoType:
     case Value::Kind::VariableType:
-      CARBON_FATAL() << "pattern type in alias target";
+      CARBON_FATAL() << "pattern type in alias target: " << *type;
 
     case Value::Kind::IntType:
     case Value::Kind::BoolType:
@@ -6198,6 +6197,7 @@ static auto IsValidTypeForAliasTarget(Nonnull<const Value*> type) -> bool {
     case Value::Kind::ChoiceType:
     case Value::Kind::StringType:
     case Value::Kind::AssociatedConstant:
+    case Value::Kind::TypeOfMixinPseudoType:
       return false;
 
     case Value::Kind::FunctionType:
diff --git a/explorer/testdata/mixin/fail_mix_as_alias_target.carbon b/explorer/testdata/mixin/fail_mix_as_alias_target.carbon
new file mode 100644
index 000000000000..7297be1d68f7
--- /dev/null
+++ b/explorer/testdata/mixin/fail_mix_as_alias_target.carbon
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+package ExplorerTest api;
+
+__mixin Operations {}
+
+// CHECK:STDERR: COMPILATION ERROR: fail_mix_as_alias_target.carbon:[[@LINE+1]]: invalid target for alias declaration
+alias OperationsAlias = Operations;
+
+fn Main() -> i32 {
+   return 0;
+}