@@ -5058,15 +5058,31 @@ function tryMerge(older: Element, newer: Element): DeclaredElement | null {
 
 /** Copies the members of `src` to `dest`. */
 function copyMembers(src: Element, dest: Element): void {
+  let program = src.program;
+  assert(program == dest.program);
+
   let srcMembers = src.members;
   if (srcMembers) {
     let destMembers = dest.members;
     if (!destMembers) dest.members = destMembers = new Map();
     // TODO: for (let [memberName, member] of srcMembers) {
     for (let _keys = Map_keys(srcMembers), i = 0, k = _keys.length; i < k; ++i) {
       let memberName = unchecked(_keys[i]);
-      let member = assert(srcMembers.get(memberName));
-      destMembers.set(memberName, member);
+      let srcMember = assert(srcMembers.get(memberName));
+      // This isn't TS compatible in every case, but the logic involved in
+      // merging, scoping, and making internal names is not currently able to
+      // handle duplicates well.
+      if (destMembers.has(memberName)) {
+        let destMember = assert(destMembers.get(memberName));
+        program.errorRelated(
+          DiagnosticCode.Duplicate_identifier_0,
+          srcMember.declaration.name.range, destMember.declaration.name.range,
+          memberName
+        );
+        continue;
+      }
+
+      destMembers.set(memberName, srcMember);
     }
   }
 }
 
@@ -0,0 +1,13 @@
+{
+    "stderr": [
+        "Duplicate identifier 'bar'.",
+        "in issues/2793.ts(8,14)",
+        "in issues/2793.ts(2,10)",
+        "Duplicate identifier 'baz'.",
+        "in issues/2793.ts(9,7)",
+        "in issues/2793.ts(3,10)",
+        "Duplicate identifier 'qux'.",
+        "in issues/2793.ts(10,14)",
+        "in issues/2793.ts(4,18)"
+    ]
+}
@@ -0,0 +1,12 @@
+class Foo {
+  static bar: i32 = 2; // errors in TS
+  static baz: i32 = 2; // does not error in TS
+  private static qux: i32 = 2; // errors in TS
+}
+
+namespace Foo {
+  export let bar: i32 = 1;
+  let baz: string = "baz";
+  export let qux: i32 = 1;
+  let hi: i32 = 1;
+}