diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index e1bb95481a1..d8caea1fde8 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -2633,7 +2633,8 @@ namespace ts {
             // If needed, we should emit a variable declaration for the enum. If we emit
             // a leading variable declaration, we should not emit leading comments for the
             // enum body.
-            if (addVarForEnumOrModuleDeclaration(statements, node)) {
+            const varAdded = addVarForEnumOrModuleDeclaration(statements, node);
+            if (varAdded) {
                 // We should still emit the comments if we are emitting a system module.
                 if (moduleKind !== ModuleKind.System || currentLexicalScope !== currentSourceFile) {
                     emitFlags |= EmitFlags.NoLeadingComments;
@@ -2691,8 +2692,13 @@ namespace ts {
             );
 
             setOriginalNode(enumStatement, node);
+            if (varAdded) {
+                // If a variable was added, synthetic comments are mitted on it, not on the moduleStatement.
+                setSyntheticLeadingComments(enumStatement, undefined);
+                setSyntheticTrailingComments(enumStatement, undefined);
+            }
             setTextRange(enumStatement, node);
-            setEmitFlags(enumStatement, emitFlags);
+            addEmitFlags(enumStatement, emitFlags);
             statements.push(enumStatement);
 
             // Add a DeclarationMarker for the enum to preserve trailing comments and mark
@@ -2882,7 +2888,7 @@ namespace ts {
                 //     })(m1 || (m1 = {})); // trailing comment module
                 //
                 setCommentRange(statement, node);
-                setEmitFlags(statement, EmitFlags.NoTrailingComments | EmitFlags.HasEndOfDeclarationMarker);
+                addEmitFlags(statement, EmitFlags.NoTrailingComments | EmitFlags.HasEndOfDeclarationMarker);
                 statements.push(statement);
                 return true;
             }
@@ -2922,7 +2928,8 @@ namespace ts {
             // If needed, we should emit a variable declaration for the module. If we emit
             // a leading variable declaration, we should not emit leading comments for the
             // module body.
-            if (addVarForEnumOrModuleDeclaration(statements, node)) {
+            const varAdded = addVarForEnumOrModuleDeclaration(statements, node);
+            if (varAdded) {
                 // We should still emit the comments if we are emitting a system module.
                 if (moduleKind !== ModuleKind.System || currentLexicalScope !== currentSourceFile) {
                     emitFlags |= EmitFlags.NoLeadingComments;
@@ -2979,8 +2986,13 @@ namespace ts {
             );
 
             setOriginalNode(moduleStatement, node);
+            if (varAdded) {
+                // If a variable was added, synthetic comments are mitted on it, not on the moduleStatement.
+                setSyntheticLeadingComments(moduleStatement, undefined);
+                setSyntheticTrailingComments(moduleStatement, undefined);
+            }
             setTextRange(moduleStatement, node);
-            setEmitFlags(moduleStatement, emitFlags);
+            addEmitFlags(moduleStatement, emitFlags);
             statements.push(moduleStatement);
 
             // Add a DeclarationMarker for the namespace to preserve trailing comments and mark
diff --git a/src/testRunner/unittests/transform.ts b/src/testRunner/unittests/transform.ts
index d2a61fb1248..31422003b44 100644
--- a/src/testRunner/unittests/transform.ts
+++ b/src/testRunner/unittests/transform.ts
@@ -357,6 +357,27 @@ class Clazz {
                         }
                     }).outputText;
         });
+
+        testBaseline("transformAddCommentToNamespace", () => {
+            return transpileModule(`
+// namespace comment.
+namespace Foo {
+    export const x = 1;
+}
+// another comment.
+namespace Foo {
+    export const y = 1;
+}
+`, {
+                        transformers: {
+                            before: [addSyntheticComment(n => isModuleDeclaration(n))],
+                        },
+                        compilerOptions: {
+                            target: ScriptTarget.ES2015,
+                            newLine: NewLineKind.CarriageReturnLineFeed,
+                        }
+                    }).outputText;
+        });
     });
 }
 
diff --git a/tests/baselines/reference/transformApi/transformsCorrectly.transformAddCommentToNamespace.js b/tests/baselines/reference/transformApi/transformsCorrectly.transformAddCommentToNamespace.js
new file mode 100644
index 00000000000..d2a32d437fa
--- /dev/null
+++ b/tests/baselines/reference/transformApi/transformsCorrectly.transformAddCommentToNamespace.js
@@ -0,0 +1,9 @@
+/*comment*/
+var Foo;
+(function (Foo) {
+    Foo.x = 1;
+})(Foo || (Foo = {}));
+/*comment*/
+(function (Foo) {
+    Foo.y = 1;
+})(Foo || (Foo = {}));