diff --git a/javascript/ql/src/semmle/javascript/AST.qll b/javascript/ql/src/semmle/javascript/AST.qll
index 81bb64f272c..364c7ce9af9 100644
--- a/javascript/ql/src/semmle/javascript/AST.qll
+++ b/javascript/ql/src/semmle/javascript/AST.qll
@@ -125,6 +125,42 @@ class ASTNode extends @ast_node, Locatable {
   /** Holds if this syntactic entity belongs to an externs file. */
   predicate inExternsFile() { getTopLevel().isExterns() }
 
+  /**
+   * Holds if this is an ambient node that is not a `TypeExpr` and is not inside a `.d.ts` file
+   *
+   * Since the overwhelming majority of ambient nodes are `TypeExpr` or inside `.d.ts` files,
+   * we avoid caching them.
+   */
+  cached
+  private predicate isAmbientInternal() {
+    getParent().isAmbientInternal()
+    or
+    not isAmbientTopLevel(getTopLevel()) and
+    (
+      this instanceof ExternalModuleDeclaration
+      or
+      this instanceof GlobalAugmentationDeclaration
+      or
+      this instanceof ExportAsNamespaceDeclaration
+      or
+      this instanceof TypeAliasDeclaration
+      or
+      this instanceof InterfaceDeclaration
+      or
+      hasDeclareKeyword(this)
+      or
+      hasTypeKeyword(this)
+      or
+      // An export such as `export declare function f()` should be seen as ambient.
+      hasDeclareKeyword(this.(ExportNamedDeclaration).getOperand())
+      or
+      exists(Function f |
+        this = f and
+        not f.hasBody()
+      )
+    )
+  }
+
   /**
    * Holds if this is part of an ambient declaration or type annotation in a TypeScript file.
    *
@@ -134,9 +170,22 @@ class ASTNode extends @ast_node, Locatable {
    * The TypeScript compiler emits no code for ambient declarations, but they
    * can affect name resolution and type checking at compile-time.
    */
-  predicate isAmbient() { getParent().isAmbient() }
+  pragma[inline]
+  predicate isAmbient() {
+    isAmbientInternal()
+    or
+    isAmbientTopLevel(getTopLevel())
+    or
+    this instanceof TypeExpr
+  }
 }
 
+/**
+ * Holds if the given file is a `.d.ts` file.
+ */
+cached
+private predicate isAmbientTopLevel(TopLevel tl) { tl.getFile().getBaseName().matches("%.d.ts") }
+
 /**
  * A toplevel syntactic unit; that is, a stand-alone script, an inline script
  * embedded in an HTML `<script>` tag, a code snippet assigned to an HTML event
@@ -197,11 +246,6 @@ class TopLevel extends @toplevel, StmtContainer {
   override ControlFlowNode getFirstControlFlowNode() { result = getEntry() }
 
   override string toString() { result = "<toplevel>" }
-
-  override predicate isAmbient() {
-    getFile().getFileType().isTypeScript() and
-    getFile().getBaseName().matches("%.d.ts")
-  }
 }
 
 /**
diff --git a/javascript/ql/src/semmle/javascript/Classes.qll b/javascript/ql/src/semmle/javascript/Classes.qll
index e93e0565ce8..ca2ffd20bc4 100644
--- a/javascript/ql/src/semmle/javascript/Classes.qll
+++ b/javascript/ql/src/semmle/javascript/Classes.qll
@@ -1059,12 +1059,6 @@ class FieldDeclaration extends MemberDeclaration, @field {
 
   /** Holds if this is a TypeScript field marked as definitely assigned with the `!` operator. */
   predicate hasDefiniteAssignmentAssertion() { hasDefiniteAssignmentAssertion(this) }
-
-  override predicate isAmbient() {
-    hasDeclareKeyword(this)
-    or
-    getParent().isAmbient()
-  }
 }
 
 /**
diff --git a/javascript/ql/src/semmle/javascript/ES2015Modules.qll b/javascript/ql/src/semmle/javascript/ES2015Modules.qll
index df094df2952..256bbf70064 100644
--- a/javascript/ql/src/semmle/javascript/ES2015Modules.qll
+++ b/javascript/ql/src/semmle/javascript/ES2015Modules.qll
@@ -79,11 +79,6 @@ class ImportDeclaration extends Stmt, Import, @importdeclaration {
 
   /** Holds if this is declared with the `type` keyword, so it only imports types. */
   predicate isTypeOnly() { hasTypeKeyword(this) }
-
-  override predicate isAmbient() {
-    Stmt.super.isAmbient() or
-    isTypeOnly()
-  }
 }
 
 /** A literal path expression appearing in an `import` declaration. */
@@ -267,11 +262,6 @@ abstract class ExportDeclaration extends Stmt, @exportdeclaration {
 
   /** Holds if is declared with the `type` keyword, so only types are exported. */
   predicate isTypeOnly() { hasTypeKeyword(this) }
-
-  override predicate isAmbient() {
-    Stmt.super.isAmbient() or
-    isTypeOnly()
-  }
 }
 
 /**
@@ -422,11 +412,6 @@ class ExportNamedDeclaration extends ExportDeclaration, @exportnameddeclaration
 
   /** Gets an export specifier of this declaration. */
   ExportSpecifier getASpecifier() { result = getSpecifier(_) }
-
-  override predicate isAmbient() {
-    // An export such as `export declare function f()` should be seen as ambient.
-    hasDeclareKeyword(getOperand()) or getParent().isAmbient()
-  }
 }
 
 /**
diff --git a/javascript/ql/src/semmle/javascript/Functions.qll b/javascript/ql/src/semmle/javascript/Functions.qll
index 719e094dfc0..5a915089697 100644
--- a/javascript/ql/src/semmle/javascript/Functions.qll
+++ b/javascript/ql/src/semmle/javascript/Functions.qll
@@ -397,8 +397,6 @@ class Function extends @function, Parameterized, TypeParameterized, StmtContaine
    */
   predicate isAbstract() { exists(MethodDeclaration md | this = md.getBody() | md.isAbstract()) }
 
-  override predicate isAmbient() { getParent().isAmbient() or not hasBody() }
-
   /**
    * Holds if this function cannot be invoked using `new` because it
    * is of the given `kind`.
diff --git a/javascript/ql/src/semmle/javascript/Stmt.qll b/javascript/ql/src/semmle/javascript/Stmt.qll
index 7ec69344aa7..6b3d6e35d32 100644
--- a/javascript/ql/src/semmle/javascript/Stmt.qll
+++ b/javascript/ql/src/semmle/javascript/Stmt.qll
@@ -54,8 +54,6 @@ class Stmt extends @stmt, ExprOrStmt, Documentable {
     getContainer().(Expr).getEnclosingStmt().nestedIn(outer)
   }
 
-  override predicate isAmbient() { hasDeclareKeyword(this) or getParent().isAmbient() }
-
   /**
    * Gets the `try` statement with a catch block containing this statement without
    * crossing function boundaries or other `try ` statements with catch blocks.
@@ -931,8 +929,6 @@ class DebuggerStmt extends @debuggerstmt, Stmt {
  */
 class FunctionDeclStmt extends @functiondeclstmt, Stmt, Function {
   override Stmt getEnclosingStmt() { result = this }
-
-  override predicate isAmbient() { Function.super.isAmbient() }
 }
 
 /**
diff --git a/javascript/ql/src/semmle/javascript/TypeScript.qll b/javascript/ql/src/semmle/javascript/TypeScript.qll
index c6497355763..0bf8ab2faf0 100644
--- a/javascript/ql/src/semmle/javascript/TypeScript.qll
+++ b/javascript/ql/src/semmle/javascript/TypeScript.qll
@@ -155,8 +155,6 @@ class ExternalModuleDeclaration extends Stmt, StmtContainer, @externalmoduledecl
   int getNumStmt() { result = count(getAStmt()) }
 
   override StmtContainer getEnclosingContainer() { result = this.getContainer() }
-
-  override predicate isAmbient() { any() }
 }
 
 /**
@@ -176,8 +174,6 @@ class GlobalAugmentationDeclaration extends Stmt, StmtContainer, @globalaugmenta
   int getNumStmt() { result = count(getAStmt()) }
 
   override StmtContainer getEnclosingContainer() { result = this.getContainer() }
-
-  override predicate isAmbient() { any() }
 }
 
 /** A TypeScript "import-equals" declaration. */
@@ -237,8 +233,6 @@ class ExportAsNamespaceDeclaration extends Stmt, @exportasnamespacedeclaration {
    * Gets the `X` in `export as namespace X`.
    */
   Identifier getIdentifier() { result = getChildExpr(0) }
-
-  override predicate isAmbient() { any() }
 }
 
 /**
@@ -259,8 +253,6 @@ class TypeAliasDeclaration extends @typealiasdeclaration, TypeParameterized, Stm
 
   override string describe() { result = "type alias " + getName() }
 
-  override predicate isAmbient() { any() }
-
   /**
    * Gets the canonical name of the type being defined.
    */
@@ -286,8 +278,6 @@ class InterfaceDeclaration extends Stmt, InterfaceDefinition, @interfacedeclarat
 
   override StmtContainer getContainer() { result = Stmt.super.getContainer() }
 
-  override predicate isAmbient() { any() }
-
   override string describe() { result = "interface " + getName() }
 
   /**
@@ -533,8 +523,6 @@ class LocalNamespaceName extends @local_namespace_name, LexicalName {
 class TypeExpr extends ExprOrType, @typeexpr, TypeAnnotation {
   override string toString() { typeexprs(this, _, _, _, result) }
 
-  override predicate isAmbient() { any() }
-
   /**
    * Gets the static type expressed by this type annotation.
    *
@@ -1410,8 +1398,6 @@ class EnumDeclaration extends NamespaceDefinition, @enumdeclaration, AST::ValueN
   /** Holds if this enumeration is declared with the `const` keyword. */
   predicate isConst() { isConstEnum(this) }
 
-  override predicate isAmbient() { hasDeclareKeyword(this) or getParent().isAmbient() }
-
   override ControlFlowNode getFirstControlFlowNode() { result = getIdentifier() }
 }