diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 5f88cd7bebc..3c1c83cb216 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -32802,7 +32802,7 @@ namespace ts {
                         Diagnostics.An_index_signature_parameter_type_cannot_be_a_union_type_Consider_using_a_mapped_object_type_instead);
                 }
 
-                return grammarErrorOnNode(parameter.name, Diagnostics.An_index_signature_parameter_type_must_be_string_or_number);
+                return grammarErrorOnNode(parameter.name, Diagnostics.An_index_signature_parameter_type_must_be_either_string_or_number);
             }
             if (!node.type) {
                 return grammarErrorOnNode(node, Diagnostics.An_index_signature_must_have_a_type_annotation);