diff --git a/src/class-elements/grammar-private-environment-on-class-heritage.case b/src/class-elements/grammar-private-environment-on-class-heritage.case
new file mode 100644
index 0000000000..c961ccc762
--- /dev/null
+++ b/src/class-elements/grammar-private-environment-on-class-heritage.case
@@ -0,0 +1,34 @@
+// Copyright (C) 2019 Caio Lima (Igalia S.L). All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+desc: It's a SyntaxError if a class expression evaluated on ClassHeritage uses an undeclared private name.
+info: |
+    Runtime Semantics: ClassDefinitionEvaluation
+
+    ClassTail : ClassHeritage { ClassBody }
+        ...
+        5. Let outerPrivateEnvironment be the PrivateEnvironment of the running execution context.
+        6. Let classPrivateEnvironment be NewDeclarativeEnvironment(outerPrivateEnvironment).
+        7. Let classPrivateEnvRec be classPrivateEnvironment's EnvironmentRecord.
+        8. If ClassBodyopt is present, then
+            a. For each element dn of the PrivateBoundIdentifiers of ClassBodyopt,
+              i. Perform classPrivateEnvRec.CreateImmutableBinding(dn, true).
+        9. If ClassHeritageopt is not present, then
+            a. Let protoParent be the intrinsic object %ObjectPrototype%.
+            b. Let constructorParent be the intrinsic object %FunctionPrototype%.
+        10. Else,
+            a. Set the running execution context's LexicalEnvironment to classScope.
+            b. NOTE: The running execution context's PrivateEnvironment is outerPrivateEnvironment when evaluating ClassHeritage.
+        ...
+template: syntax/invalid
+features: [class-fields-private, class-fields-public]
+---*/
+
+//- heritage
+
+extends class { x = this.#foo; }
+
+//- elements
+
+#foo;
diff --git a/test/language/expressions/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js b/test/language/expressions/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js
new file mode 100644
index 0000000000..7089a34ed2
--- /dev/null
+++ b/test/language/expressions/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js
@@ -0,0 +1,39 @@
+// This file was procedurally generated from the following sources:
+// - src/class-elements/grammar-private-environment-on-class-heritage.case
+// - src/class-elements/syntax/invalid/cls-expr-elements-invalid-syntax.template
+/*---
+description: It's a SyntaxError if a class expression evaluated on ClassHeritage uses an undeclared private name. (class expression)
+esid: prod-ClassElement
+features: [class-fields-private, class-fields-public, class]
+flags: [generated]
+negative:
+  phase: parse
+  type: SyntaxError
+info: |
+    Runtime Semantics: ClassDefinitionEvaluation
+
+    ClassTail : ClassHeritage { ClassBody }
+        ...
+        5. Let outerPrivateEnvironment be the PrivateEnvironment of the running execution context.
+        6. Let classPrivateEnvironment be NewDeclarativeEnvironment(outerPrivateEnvironment).
+        7. Let classPrivateEnvRec be classPrivateEnvironment's EnvironmentRecord.
+        8. If ClassBodyopt is present, then
+            a. For each element dn of the PrivateBoundIdentifiers of ClassBodyopt,
+              i. Perform classPrivateEnvRec.CreateImmutableBinding(dn, true).
+        9. If ClassHeritageopt is not present, then
+            a. Let protoParent be the intrinsic object %ObjectPrototype%.
+            b. Let constructorParent be the intrinsic object %FunctionPrototype%.
+        10. Else,
+            a. Set the running execution context's LexicalEnvironment to classScope.
+            b. NOTE: The running execution context's PrivateEnvironment is outerPrivateEnvironment when evaluating ClassHeritage.
+        ...
+
+---*/
+
+
+$DONOTEVALUATE();
+
+var C = class extends class { x = this.#foo; }
+{
+  #foo;
+};
diff --git a/test/language/statements/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js b/test/language/statements/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js
new file mode 100644
index 0000000000..a4731a80c3
--- /dev/null
+++ b/test/language/statements/class/elements/syntax/early-errors/grammar-private-environment-on-class-heritage.js
@@ -0,0 +1,39 @@
+// This file was procedurally generated from the following sources:
+// - src/class-elements/grammar-private-environment-on-class-heritage.case
+// - src/class-elements/syntax/invalid/cls-decl-elements-invalid-syntax.template
+/*---
+description: It's a SyntaxError if a class expression evaluated on ClassHeritage uses an undeclared private name. (class declaration)
+esid: prod-ClassElement
+features: [class-fields-private, class-fields-public, class]
+flags: [generated]
+negative:
+  phase: parse
+  type: SyntaxError
+info: |
+    Runtime Semantics: ClassDefinitionEvaluation
+
+    ClassTail : ClassHeritage { ClassBody }
+        ...
+        5. Let outerPrivateEnvironment be the PrivateEnvironment of the running execution context.
+        6. Let classPrivateEnvironment be NewDeclarativeEnvironment(outerPrivateEnvironment).
+        7. Let classPrivateEnvRec be classPrivateEnvironment's EnvironmentRecord.
+        8. If ClassBodyopt is present, then
+            a. For each element dn of the PrivateBoundIdentifiers of ClassBodyopt,
+              i. Perform classPrivateEnvRec.CreateImmutableBinding(dn, true).
+        9. If ClassHeritageopt is not present, then
+            a. Let protoParent be the intrinsic object %ObjectPrototype%.
+            b. Let constructorParent be the intrinsic object %FunctionPrototype%.
+        10. Else,
+            a. Set the running execution context's LexicalEnvironment to classScope.
+            b. NOTE: The running execution context's PrivateEnvironment is outerPrivateEnvironment when evaluating ClassHeritage.
+        ...
+
+---*/
+
+
+$DONOTEVALUATE();
+
+class C extends class { x = this.#foo; }
+{
+  #foo;
+}