diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/input.js
new file mode 100644
index 000000000000..e4e3ae4c3870
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/input.js
@@ -0,0 +1,9 @@
+class B {
+  meth() {
+    class A {
+      #x = this.#y;
+    }
+  }
+
+  #y;
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/options.json
new file mode 100644
index 000000000000..25819769bb20
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/options.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["classPrivateProperties"]
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/output.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/output.json
new file mode 100644
index 000000000000..1bd1092fae92
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-outer-class/output.json
@@ -0,0 +1,352 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 73,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 9,
+      "column": 1
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 73,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 9,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start": 0,
+        "end": 73,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 9,
+            "column": 1
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 6,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 6
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            },
+            "identifierName": "B"
+          },
+          "name": "B"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start": 8,
+          "end": 73,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 8
+            },
+            "end": {
+              "line": 9,
+              "column": 1
+            }
+          },
+          "body": [
+            {
+              "type": "ClassMethod",
+              "start": 12,
+              "end": 64,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 2
+                },
+                "end": {
+                  "line": 6,
+                  "column": 3
+                }
+              },
+              "static": false,
+              "key": {
+                "type": "Identifier",
+                "start": 12,
+                "end": 16,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 6
+                  },
+                  "identifierName": "meth"
+                },
+                "name": "meth"
+              },
+              "computed": false,
+              "kind": "method",
+              "id": null,
+              "generator": false,
+              "async": false,
+              "params": [],
+              "body": {
+                "type": "BlockStatement",
+                "start": 19,
+                "end": 64,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 9
+                  },
+                  "end": {
+                    "line": 6,
+                    "column": 3
+                  }
+                },
+                "body": [
+                  {
+                    "type": "ClassDeclaration",
+                    "start": 25,
+                    "end": 60,
+                    "loc": {
+                      "start": {
+                        "line": 3,
+                        "column": 4
+                      },
+                      "end": {
+                        "line": 5,
+                        "column": 5
+                      }
+                    },
+                    "id": {
+                      "type": "Identifier",
+                      "start": 31,
+                      "end": 32,
+                      "loc": {
+                        "start": {
+                          "line": 3,
+                          "column": 10
+                        },
+                        "end": {
+                          "line": 3,
+                          "column": 11
+                        },
+                        "identifierName": "A"
+                      },
+                      "name": "A"
+                    },
+                    "superClass": null,
+                    "body": {
+                      "type": "ClassBody",
+                      "start": 33,
+                      "end": 60,
+                      "loc": {
+                        "start": {
+                          "line": 3,
+                          "column": 12
+                        },
+                        "end": {
+                          "line": 5,
+                          "column": 5
+                        }
+                      },
+                      "body": [
+                        {
+                          "type": "ClassPrivateProperty",
+                          "start": 41,
+                          "end": 54,
+                          "loc": {
+                            "start": {
+                              "line": 4,
+                              "column": 6
+                            },
+                            "end": {
+                              "line": 4,
+                              "column": 19
+                            }
+                          },
+                          "static": false,
+                          "key": {
+                            "type": "PrivateName",
+                            "start": 41,
+                            "end": 43,
+                            "loc": {
+                              "start": {
+                                "line": 4,
+                                "column": 6
+                              },
+                              "end": {
+                                "line": 4,
+                                "column": 8
+                              }
+                            },
+                            "id": {
+                              "type": "Identifier",
+                              "start": 42,
+                              "end": 43,
+                              "loc": {
+                                "start": {
+                                  "line": 4,
+                                  "column": 7
+                                },
+                                "end": {
+                                  "line": 4,
+                                  "column": 8
+                                },
+                                "identifierName": "x"
+                              },
+                              "name": "x"
+                            }
+                          },
+                          "value": {
+                            "type": "MemberExpression",
+                            "start": 46,
+                            "end": 53,
+                            "loc": {
+                              "start": {
+                                "line": 4,
+                                "column": 11
+                              },
+                              "end": {
+                                "line": 4,
+                                "column": 18
+                              }
+                            },
+                            "object": {
+                              "type": "ThisExpression",
+                              "start": 46,
+                              "end": 50,
+                              "loc": {
+                                "start": {
+                                  "line": 4,
+                                  "column": 11
+                                },
+                                "end": {
+                                  "line": 4,
+                                  "column": 15
+                                }
+                              }
+                            },
+                            "property": {
+                              "type": "PrivateName",
+                              "start": 51,
+                              "end": 53,
+                              "loc": {
+                                "start": {
+                                  "line": 4,
+                                  "column": 16
+                                },
+                                "end": {
+                                  "line": 4,
+                                  "column": 18
+                                }
+                              },
+                              "id": {
+                                "type": "Identifier",
+                                "start": 52,
+                                "end": 53,
+                                "loc": {
+                                  "start": {
+                                    "line": 4,
+                                    "column": 17
+                                  },
+                                  "end": {
+                                    "line": 4,
+                                    "column": 18
+                                  },
+                                  "identifierName": "y"
+                                },
+                                "name": "y"
+                              }
+                            },
+                            "computed": false
+                          }
+                        }
+                      ]
+                    }
+                  }
+                ],
+                "directives": []
+              }
+            },
+            {
+              "type": "ClassPrivateProperty",
+              "start": 68,
+              "end": 71,
+              "loc": {
+                "start": {
+                  "line": 8,
+                  "column": 2
+                },
+                "end": {
+                  "line": 8,
+                  "column": 5
+                }
+              },
+              "static": false,
+              "key": {
+                "type": "PrivateName",
+                "start": 68,
+                "end": 70,
+                "loc": {
+                  "start": {
+                    "line": 8,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 8,
+                    "column": 4
+                  }
+                },
+                "id": {
+                  "type": "Identifier",
+                  "start": 69,
+                  "end": 70,
+                  "loc": {
+                    "start": {
+                      "line": 8,
+                      "column": 3
+                    },
+                    "end": {
+                      "line": 8,
+                      "column": 4
+                    },
+                    "identifierName": "y"
+                  },
+                  "name": "y"
+                }
+              },
+              "value": null
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/input.js
new file mode 100644
index 000000000000..bd7c6a515696
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/input.js
@@ -0,0 +1,4 @@
+class A {
+  #x = this.#y;
+  #y;
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/options.json
new file mode 100644
index 000000000000..25819769bb20
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/options.json
@@ -0,0 +1,3 @@
+{
+  "plugins": ["classPrivateProperties"]
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/output.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/output.json
new file mode 100644
index 000000000000..3c7ad5de9321
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/declared-later-same-class/output.json
@@ -0,0 +1,245 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 33,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 4,
+      "column": 1
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 33,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 4,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start": 0,
+        "end": 33,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 4,
+            "column": 1
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 6,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 6
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            },
+            "identifierName": "A"
+          },
+          "name": "A"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start": 8,
+          "end": 33,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 8
+            },
+            "end": {
+              "line": 4,
+              "column": 1
+            }
+          },
+          "body": [
+            {
+              "type": "ClassPrivateProperty",
+              "start": 12,
+              "end": 25,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 2
+                },
+                "end": {
+                  "line": 2,
+                  "column": 15
+                }
+              },
+              "static": false,
+              "key": {
+                "type": "PrivateName",
+                "start": 12,
+                "end": 14,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 4
+                  }
+                },
+                "id": {
+                  "type": "Identifier",
+                  "start": 13,
+                  "end": 14,
+                  "loc": {
+                    "start": {
+                      "line": 2,
+                      "column": 3
+                    },
+                    "end": {
+                      "line": 2,
+                      "column": 4
+                    },
+                    "identifierName": "x"
+                  },
+                  "name": "x"
+                }
+              },
+              "value": {
+                "type": "MemberExpression",
+                "start": 17,
+                "end": 24,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 7
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 14
+                  }
+                },
+                "object": {
+                  "type": "ThisExpression",
+                  "start": 17,
+                  "end": 21,
+                  "loc": {
+                    "start": {
+                      "line": 2,
+                      "column": 7
+                    },
+                    "end": {
+                      "line": 2,
+                      "column": 11
+                    }
+                  }
+                },
+                "property": {
+                  "type": "PrivateName",
+                  "start": 22,
+                  "end": 24,
+                  "loc": {
+                    "start": {
+                      "line": 2,
+                      "column": 12
+                    },
+                    "end": {
+                      "line": 2,
+                      "column": 14
+                    }
+                  },
+                  "id": {
+                    "type": "Identifier",
+                    "start": 23,
+                    "end": 24,
+                    "loc": {
+                      "start": {
+                        "line": 2,
+                        "column": 13
+                      },
+                      "end": {
+                        "line": 2,
+                        "column": 14
+                      },
+                      "identifierName": "y"
+                    },
+                    "name": "y"
+                  }
+                },
+                "computed": false
+              }
+            },
+            {
+              "type": "ClassPrivateProperty",
+              "start": 28,
+              "end": 31,
+              "loc": {
+                "start": {
+                  "line": 3,
+                  "column": 2
+                },
+                "end": {
+                  "line": 3,
+                  "column": 5
+                }
+              },
+              "static": false,
+              "key": {
+                "type": "PrivateName",
+                "start": 28,
+                "end": 30,
+                "loc": {
+                  "start": {
+                    "line": 3,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 3,
+                    "column": 4
+                  }
+                },
+                "id": {
+                  "type": "Identifier",
+                  "start": 29,
+                  "end": 30,
+                  "loc": {
+                    "start": {
+                      "line": 3,
+                      "column": 3
+                    },
+                    "end": {
+                      "line": 3,
+                      "column": 4
+                    },
+                    "identifierName": "y"
+                  },
+                  "name": "y"
+                }
+              },
+              "value": null
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/input.js
new file mode 100644
index 000000000000..3177068d7eb0
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/input.js
@@ -0,0 +1,6 @@
+class A {
+  #x;
+  meth() {
+    var prop = foo.#priv;
+  }
+}
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/options.json
new file mode 100644
index 000000000000..f5d54118131a
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-nested/options.json
@@ -0,0 +1,4 @@
+{
+  "plugins": ["classPrivateProperties"],
+  "throws": "Private name #priv is not defined (4:19)"
+}
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/input.js
new file mode 100644
index 000000000000..10607b89b6db
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/input.js
@@ -0,0 +1 @@
+var prop = foo.#priv;
\ No newline at end of file
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/options.json
new file mode 100644
index 000000000000..9682fa229092
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/undeclared-top-level/options.json
@@ -0,0 +1,4 @@
+{
+  "plugins": ["classPrivateProperties"],
+  "throws": "Unexpected character '#' (1:15)"
+}
\ No newline at end of file