diff --git a/packages/babel-parser/src/parser/expression.js b/packages/babel-parser/src/parser/expression.js
index 48dd82d673..e1ea1aa55d 100644
--- a/packages/babel-parser/src/parser/expression.js
+++ b/packages/babel-parser/src/parser/expression.js
@@ -923,7 +923,19 @@ export default class ExpressionParser extends LValParser {
     if (isPrivate) {
       this.expectOnePlugin(["classPrivateProperties", "classPrivateMethods"]);
       const node = this.startNode();
+      const columnHashEnd = this.state.end;
       this.next();
+      const columnIdentifierStart = this.state.start;
+
+      const spacesBetweenHashAndIdentifier =
+        columnIdentifierStart - columnHashEnd;
+      if (spacesBetweenHashAndIdentifier != 0) {
+        this.raise(
+          columnIdentifierStart,
+          "Unexpected space between # and identifier",
+        );
+      }
+
       node.id = this.parseIdentifier(true);
       return this.finishNode(node, "PrivateName");
     } else {
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/input.js
new file mode 100644
index 0000000000..b49e1327f4
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/input.js
@@ -0,0 +1,5 @@
+class Spaces {
+  #  wrongSpaces() {
+    return fail();
+  }
+}
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/options.json
new file mode 100644
index 0000000000..f8dba0c322
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-methods/failure-spaces/options.json
@@ -0,0 +1,4 @@
+{
+  "throws": "Unexpected space between # and identifier (2:5)",
+  "plugins": ["classPrivateMethods"]
+}
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/input.js b/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/input.js
new file mode 100644
index 0000000000..023684c53e
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/input.js
@@ -0,0 +1,3 @@
+class Spaces {
+  #  wrongSpaces;
+}
diff --git a/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/options.json b/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/options.json
new file mode 100644
index 0000000000..f8dba0c322
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-spaces/options.json
@@ -0,0 +1,4 @@
+{
+  "throws": "Unexpected space between # and identifier (2:5)",
+  "plugins": ["classPrivateMethods"]
+}