diff --git a/ql/ql/src/codeql_ql/ast/Ast.qll b/ql/ql/src/codeql_ql/ast/Ast.qll
index 51ddcf0cf59..85082c3e6b7 100644
--- a/ql/ql/src/codeql_ql/ast/Ast.qll
+++ b/ql/ql/src/codeql_ql/ast/Ast.qll
@@ -500,11 +500,11 @@ class PredicateExpr extends TPredicateExpr, AstNode {
  * A classless predicate.
  */
 class ClasslessPredicate extends TClasslessPredicate, Predicate, ModuleDeclaration {
-  QL::ClasslessPredicate pred;
+  Mocks::ClasslessPredicateOrMock pred;
 
   ClasslessPredicate() { this = TClasslessPredicate(pred) }
 
-  override Location getLocation() { result = pred.getName().getLocation() }
+  override Location getLocation() { result = pred.asLeft().getName().getLocation() }
 
   /**
    * Gets the aliased value if this predicate is an alias
@@ -513,25 +513,33 @@ class ClasslessPredicate extends TClasslessPredicate, Predicate, ModuleDeclarati
    */
   final AstNode getAlias() {
     exists(QL::PredicateAliasBody alias |
-      alias.getParent() = pred and
+      alias.getParent() = pred.asLeft() and
       toQL(result).getParent() = alias
     )
     or
-    toQL(result) = pred.getChild(_).(QL::HigherOrderTerm)
+    toQL(result) = pred.asLeft().getChild(_).(QL::HigherOrderTerm)
   }
 
   override string getAPrimaryQlClass() { result = "ClasslessPredicate" }
 
-  override Formula getBody() { toQL(result) = pred.getChild(_).(QL::Body).getChild() }
+  override Formula getBody() { toQL(result) = pred.asLeft().getChild(_).(QL::Body).getChild() }
 
-  override string getName() { result = pred.getName().getValue() }
+  override string getName() {
+    result = pred.asLeft().getName().getValue()
+    or
+    result = pred.asRight().getName()
+  }
 
   override VarDecl getParameter(int i) {
     toQL(result) =
-      rank[i + 1](QL::VarDecl decl, int index | decl = pred.getChild(index) | decl order by index)
+      rank[i + 1](QL::VarDecl decl, int index |
+        decl = pred.asLeft().getChild(index)
+      |
+        decl order by index
+      )
   }
 
-  override TypeExpr getReturnTypeExpr() { toQL(result) = pred.getReturnType() }
+  override TypeExpr getReturnTypeExpr() { toQL(result) = pred.asLeft().getReturnType() }
 
   override AstNode getAChild(string pred_name) {
     result = Predicate.super.getAChild(pred_name)
diff --git a/ql/ql/src/codeql_ql/ast/internal/AstMocks.qll b/ql/ql/src/codeql_ql/ast/internal/AstMocks.qll
index 70c589ab6b9..d9c2232ce09 100644
--- a/ql/ql/src/codeql_ql/ast/internal/AstMocks.qll
+++ b/ql/ql/src/codeql_ql/ast/internal/AstMocks.qll
@@ -17,7 +17,8 @@ private import codeql.util.Either
 newtype TMockAst =
   TMockModule(string id) { id instanceof MockModule::Range } or
   TMockClass(string id) { id instanceof MockClass::Range } or
-  TMockTypeExpr(string id) { id instanceof MockTypeExpr::Range }
+  TMockTypeExpr(string id) { id instanceof MockTypeExpr::Range } or
+  TMockClasslessPredicate(string id) { id instanceof MockClasslessPredicate::Range }
 
 /** Gets a mocked Ast node from the string ID that represents it. */
 MockAst fromId(string id) {
@@ -26,6 +27,8 @@ MockAst fromId(string id) {
   result = TMockClass(id)
   or
   result = TMockTypeExpr(id)
+  or
+  result = TMockClasslessPredicate(id)
   // TODO: Other nodes.
 }
 
@@ -51,7 +54,7 @@ class MockModule extends MockAst, TMockModule {
   final MockAst getMember(int i) { result = fromId(range.getMember(i)) }
 
   final predicate hasTypeParam(int i, MockAst type, string name) {
-    range.hasTypeParam(i, type.toString(), name)
+    range.hasTypeParam(i, type.getId(), name)
   }
 }
 
@@ -139,3 +142,32 @@ module MockTypeExpr {
 class TypeExprOrMock = Either<QL::TypeExpr, MockTypeExpr>::Either;
 
 class SignatureExprOrMock = Either<QL::SignatureExpr, MockSignatureExpr>::Either;
+
+/**
+ * A mocked `ClasslessPredicate`.
+ */
+class MockClasslessPredicate extends MockAst {
+  MockClasslessPredicate::Range range;
+
+  MockClasslessPredicate() { this = TMockClasslessPredicate(range) }
+
+  final string getName() { result = range.getName() }
+
+  // TODO: VarDecl.
+  final MockAst getParameter(int i) { result.getId() = range.getParameter(i) }
+}
+
+module MockClasslessPredicate {
+  abstract class Range extends string {
+    bindingset[this]
+    Range() { this = this }
+
+    /** Gets the name of the predicate. */
+    abstract string getName();
+
+    /** Gets the `i`th parameter of the predicate. */
+    abstract string getParameter(int i);
+  }
+}
+
+class ClasslessPredicateOrMock = Either<QL::ClasslessPredicate, MockClasslessPredicate>::Either;
diff --git a/ql/ql/src/codeql_ql/ast/internal/AstNodes.qll b/ql/ql/src/codeql_ql/ast/internal/AstNodes.qll
index 3b1e2ea64fc..b9d084f1b67 100644
--- a/ql/ql/src/codeql_ql/ast/internal/AstNodes.qll
+++ b/ql/ql/src/codeql_ql/ast/internal/AstNodes.qll
@@ -9,7 +9,7 @@ newtype TAstNode =
   TQLDoc(QL::Qldoc qldoc) or
   TBlockComment(QL::BlockComment comment) or
   TLineComment(QL::LineComment comment) or
-  TClasslessPredicate(QL::ClasslessPredicate pred) or
+  TClasslessPredicate(Mocks::ClasslessPredicateOrMock pred) or
   TVarDecl(QL::VarDecl decl) or
   TFieldDecl(QL::Field field) or
   TClass(Mocks::ClassOrMock cls) or
@@ -160,7 +160,7 @@ QL::AstNode toQL(AST::AstNode n) {
   or
   n = TLineComment(result)
   or
-  n = TClasslessPredicate(result)
+  n = TClasslessPredicate(any(Mocks::ClasslessPredicateOrMock m | m.asLeft() = result))
   or
   n = TVarDecl(result)
   or
@@ -213,6 +213,8 @@ Mocks::MockAst toMock(AST::AstNode n) {
   n = TClass(any(Mocks::ClassOrMock m | m.asRight() = result))
   or
   n = TType(any(Mocks::TypeExprOrMock m | m.asRight() = result))
+  or
+  n = TClasslessPredicate(any(Mocks::ClasslessPredicateOrMock m | m.asRight() = result))
 }
 
 class TPredicate =
diff --git a/ql/ql/src/codeql_ql/ast/internal/Builtins.qll b/ql/ql/src/codeql_ql/ast/internal/Builtins.qll
index f142dd5e19e..aa79fa6e195 100644
--- a/ql/ql/src/codeql_ql/ast/internal/Builtins.qll
+++ b/ql/ql/src/codeql_ql/ast/internal/Builtins.qll
@@ -150,11 +150,7 @@ module QlBuiltinsMocks {
           i = 0 and name = "MyT" and type instanceof EdgeSigType
         }
 
-        override string getMember(int i) {
-          // i = 0 and
-          // result instanceof EdgeSig::EdgeSigPredicate
-          none() // TODO:
-        }
+        override string getMember(int i) { i = 0 and result instanceof EdgeSigPred }
       }
 
       class EdgeSigType extends MockTypeExpr::Range {
@@ -162,6 +158,16 @@ module QlBuiltinsMocks {
 
         override string getClassName() { result = "MyT" }
       }
+
+      class EdgeSigPred extends MockClasslessPredicate::Range {
+        EdgeSigPred() { this = "Mock: QlBuiltins::EdgeSig::edgeSig" }
+
+        override string getName() { result = "edgeSig" }
+
+        override string getParameter(int i) {
+          none() // TODO:
+        }
+      }
     }
 
     class EquivalenceRelationModule extends MockModule::Range {