diff --git a/pkl-core/src/main/java/org/pkl/core/ast/expression/primary/ExecuteCustomThisWithRootNode.java b/pkl-core/src/main/java/org/pkl/core/ast/expression/primary/ExecuteCustomThisWithRootNode.java
index 184d8aed4..15a0f6f18 100644
--- a/pkl-core/src/main/java/org/pkl/core/ast/expression/primary/ExecuteCustomThisWithRootNode.java
+++ b/pkl-core/src/main/java/org/pkl/core/ast/expression/primary/ExecuteCustomThisWithRootNode.java
@@ -18,6 +18,7 @@ package org.pkl.core.ast.expression.primary;
 import com.oracle.truffle.api.frame.FrameDescriptor;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.DirectCallNode;
+import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.source.SourceSection;
 import org.pkl.core.ast.ExpressionNode;
 import org.pkl.core.ast.SimpleRootNode;
@@ -43,6 +44,10 @@ public final class ExecuteCustomThisWithRootNode extends ExpressionNode {
   // shouldn't be marked `@Child` because this node is actually the child of the SimpleRootNode
   // created in the constructor.
   private final ExpressionNode expressionNode;
+  private final FrameDescriptor frameDescriptor;
+  private final String qualifiedName;
+  private final int[] forGeneratorSlots;
+  private final int[] parameterSlots;
 
   public ExecuteCustomThisWithRootNode(
       SourceSection sourceSection,
@@ -53,6 +58,10 @@ public final class ExecuteCustomThisWithRootNode extends ExpressionNode {
       int[] parameterSlots) {
     super(sourceSection);
     this.expressionNode = expressionNode;
+    this.frameDescriptor = frameDescriptor;
+    this.qualifiedName = qualifiedName;
+    this.forGeneratorSlots = forGeneratorSlots;
+    this.parameterSlots = parameterSlots;
     frameDescriptor.findOrAddAuxiliarySlot(VmUtils.CUSTOM_THIS_FRAME_SLOT_ID);
     var rootNode =
         new SimpleRootNode(
@@ -68,6 +77,18 @@ public final class ExecuteCustomThisWithRootNode extends ExpressionNode {
     return expressionNode;
   }
 
+  @Override
+  public Node deepCopy() {
+    // The expression belongs to a separate root and is not copied as a child of this node.
+    return new ExecuteCustomThisWithRootNode(
+        sourceSection,
+        (ExpressionNode) expressionNode.deepCopy(),
+        frameDescriptor,
+        qualifiedName,
+        forGeneratorSlots,
+        parameterSlots);
+  }
+
   @Override
   public Object executeGeneric(VirtualFrame frame) {
     var customThis = customThisNode.executeGeneric(frame);
diff --git a/pkl-core/src/main/java/org/pkl/core/runtime/VmTypeAlias.java b/pkl-core/src/main/java/org/pkl/core/runtime/VmTypeAlias.java
index 605087360..6bcdf429c 100644
--- a/pkl-core/src/main/java/org/pkl/core/runtime/VmTypeAlias.java
+++ b/pkl-core/src/main/java/org/pkl/core/runtime/VmTypeAlias.java
@@ -19,6 +19,7 @@ import com.google.errorprone.annotations.concurrent.GuardedBy;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.frame.Frame;
 import com.oracle.truffle.api.frame.MaterializedFrame;
+import com.oracle.truffle.api.nodes.NodeVisitor;
 import com.oracle.truffle.api.source.SourceSection;
 import java.net.URI;
 import java.util.ArrayList;
@@ -30,6 +31,7 @@ import org.pkl.core.PObject;
 import org.pkl.core.TypeAlias;
 import org.pkl.core.TypeParameter;
 import org.pkl.core.ast.VmModifier;
+import org.pkl.core.ast.expression.primary.ExecuteCustomThisWithRootNode;
 import org.pkl.core.ast.type.TypeNode;
 import org.pkl.core.ast.type.TypeNode.ConstrainedTypeNode;
 import org.pkl.core.ast.type.TypeNode.TypeVariableNode;
@@ -200,25 +202,31 @@ public final class VmTypeAlias extends VmValue {
 
     var clone = (TypeNode) typeNode.deepCopy();
     clone.accept(
-        node -> {
-          if (node instanceof TypeVariableNode typeVarNode) {
-            var index = typeVarNode.getTypeParameterIndex();
-            node.replace(
-                typeArgumentNodes.length == 0
-                    ? new UnknownTypeNode(sourceSection)
-                    : deepCopy(typeArgumentNodes[index]));
-          } else if (node instanceof UnresolvedTypeNode.TypeVariable unresolvedTypeVar) {
-            // Type variables inside constraint expressions (e.g. `every((it) -> it is T)`)
-            // are still unresolved at instantiation time. Replace them with a resolved
-            // unresolved type node that returns the concrete type argument.
-            var index = unresolvedTypeVar.getTypeParameterIndex();
-            node.replace(
-                typeArgumentNodes.length == 0
-                    ? new UnresolvedTypeNode.Unknown(sourceSection)
-                    : new UnresolvedTypeNode.Resolved(
-                        sourceSection, deepCopy(typeArgumentNodes[index])));
+        new NodeVisitor() {
+          @Override
+          public boolean visit(com.oracle.truffle.api.nodes.Node node) {
+            if (node instanceof TypeVariableNode typeVarNode) {
+              var index = typeVarNode.getTypeParameterIndex();
+              node.replace(
+                  typeArgumentNodes.length == 0
+                      ? new UnknownTypeNode(sourceSection)
+                      : deepCopy(typeArgumentNodes[index]));
+            } else if (node instanceof UnresolvedTypeNode.TypeVariable unresolvedTypeVar) {
+              // Type variables inside constraint expressions (e.g. `every((it) -> it is T)`)
+              // are still unresolved at instantiation time. Replace them with a resolved
+              // unresolved type node that returns the concrete type argument.
+              var index = unresolvedTypeVar.getTypeParameterIndex();
+              node.replace(
+                  typeArgumentNodes.length == 0
+                      ? new UnresolvedTypeNode.Unknown(sourceSection)
+                      : new UnresolvedTypeNode.Resolved(
+                          sourceSection, deepCopy(typeArgumentNodes[index])));
+            } else if (node instanceof ExecuteCustomThisWithRootNode customThisNode) {
+              // A constraint with frame slots runs in a separate root, outside this tree.
+              customThisNode.getExpressionNode().accept(this);
+            }
+            return true;
           }
-          return true;
         });
 
     return clone;
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/input/types/typeAliasConstraint11.pkl b/pkl-core/src/test/files/LanguageSnippetTests/input/types/typeAliasConstraint11.pkl
new file mode 100644
index 000000000..b18c6afb8
--- /dev/null
+++ b/pkl-core/src/test/files/LanguageSnippetTests/input/types/typeAliasConstraint11.pkl
@@ -0,0 +1,14 @@
+import "pkl:test"
+
+class Foo { bar: Int }
+const function isOk(f: Foo) = f.bar > 0
+
+typealias WithInferredNew<X> = Int(isOk(new { bar = 1 }) && this is X)
+typealias WithLet<X> = Int((let (n = 1) n == 1) && this is X)
+
+wrongType = 3 is WithInferredNew<String>
+matchingType = 3 is WithInferredNew<Int>
+wrongTypeAgain = 3 is WithInferredNew<String>
+letWrongType = 3 is WithLet<String>
+letMatchingType = 3 is WithLet<Int>
+castWrongType = test.catch(() -> 3 as WithInferredNew<String>)
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/output/types/typeAliasConstraint11.pcf b/pkl-core/src/test/files/LanguageSnippetTests/output/types/typeAliasConstraint11.pcf
new file mode 100644
index 000000000..a470b7b2f
--- /dev/null
+++ b/pkl-core/src/test/files/LanguageSnippetTests/output/types/typeAliasConstraint11.pcf
@@ -0,0 +1,6 @@
+wrongType = false
+matchingType = true
+wrongTypeAgain = false
+letWrongType = false
+letMatchingType = true
+castWrongType = "Type constraint `isOk(new { bar = 1 }) && this is X` violated. Value: 3"