diff --git a/crates/oxc_transformer/src/typescript/diagnostics.rs b/crates/oxc_transformer/src/typescript/diagnostics.rs
index 7289cf3b3..53096792e 100644
--- a/crates/oxc_transformer/src/typescript/diagnostics.rs
+++ b/crates/oxc_transformer/src/typescript/diagnostics.rs
@@ -15,3 +15,8 @@ pub fn ambient_module_nested(span0: Span) -> OxcDiagnostic {
     OxcDiagnostic::warn("Ambient modules cannot be nested in other modules or namespaces.")
         .with_label(span0)
 }
+
+pub fn namespace_exporting_non_const(span0: Span) -> OxcDiagnostic {
+    OxcDiagnostic::warn("Namespaces exporting non-const are not supported by Babel. Change to const or see: https://babeljs.io/docs/en/babel-plugin-transform-typescript")
+        .with_label(span0)
+}
diff --git a/crates/oxc_transformer/src/typescript/namespace.rs b/crates/oxc_transformer/src/typescript/namespace.rs
index 6718e53f3..4e1d5a97d 100644
--- a/crates/oxc_transformer/src/typescript/namespace.rs
+++ b/crates/oxc_transformer/src/typescript/namespace.rs
@@ -1,6 +1,9 @@
 use rustc_hash::FxHashSet;
 
-use super::{diagnostics::ambient_module_nested, TypeScript};
+use super::{
+    diagnostics::{ambient_module_nested, namespace_exporting_non_const},
+    TypeScript,
+};
 
 use oxc_allocator::{Box, Vec};
 use oxc_ast::{ast::*, syntax_directed_operations::BoundNames};
@@ -238,6 +241,11 @@ impl<'a> TypeScript<'a> {
                                 );
                             }
                             Declaration::VariableDeclaration(var_decl) => {
+                                var_decl.declarations.iter().for_each(|decl| {
+                                    if !decl.kind.is_const() {
+                                        self.ctx.error(namespace_exporting_non_const(decl.span));
+                                    }
+                                });
                                 is_empty = false;
                                 let stmts = self.handle_variable_declaration(var_decl, &name);
                                 new_stmts.extend(stmts);
diff --git a/tasks/transform_conformance/babel.snap.md b/tasks/transform_conformance/babel.snap.md
index 34754d209..f95dd43eb 100644
--- a/tasks/transform_conformance/babel.snap.md
+++ b/tasks/transform_conformance/babel.snap.md
@@ -1,6 +1,6 @@
 commit: 4bd1b2c2
 
-Passed: 473/930
+Passed: 474/930
 
 # All Passed:
 * babel-preset-react
@@ -445,13 +445,12 @@ Passed: 473/930
 * opts/optimizeConstEnums/input.ts
 * opts/rewriteImportExtensions/input.ts
 
-# babel-plugin-transform-typescript (130/154)
+# babel-plugin-transform-typescript (131/154)
 * enum/mix-references/input.ts
 * enum/ts5.0-const-foldable/input.ts
 * exports/declared-types/input.ts
 * imports/type-only-export-specifier-2/input.ts
 * namespace/empty-removed/input.ts
-* namespace/mutable-fail/input.ts
 * namespace/namespace-flag/input.ts
 * namespace/nested/input.ts
 * namespace/nested-destructuring/input.ts