diff --git a/prism/diagnostic.c b/prism/diagnostic.c
index 4f9b3bf75b..957cc47d7c 100644
--- a/prism/diagnostic.c
+++ b/prism/diagnostic.c
@@ -190,7 +190,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_LEN] = {
     [PM_ERR_HASH_VALUE]                         = { "expected a value in the hash literal", PM_ERROR_LEVEL_FATAL },
     [PM_ERR_HEREDOC_TERM]                       = { "could not find a terminator for the heredoc", PM_ERROR_LEVEL_FATAL },
     [PM_ERR_INCOMPLETE_QUESTION_MARK]           = { "incomplete expression at `?`", PM_ERROR_LEVEL_FATAL },
-    [PM_ERR_INCOMPLETE_VARIABLE_CLASS]          = { "`%.*s' is not allowed as an class variable name", PM_ERROR_LEVEL_FATAL },
+    [PM_ERR_INCOMPLETE_VARIABLE_CLASS]          = { "`%.*s' is not allowed as a class variable name", PM_ERROR_LEVEL_FATAL },
     [PM_ERR_INCOMPLETE_VARIABLE_INSTANCE]       = { "`%.*s' is not allowed as an instance variable name", PM_ERROR_LEVEL_FATAL },
     [PM_ERR_INVALID_FLOAT_EXPONENT]             = { "invalid exponent", PM_ERROR_LEVEL_FATAL },
     [PM_ERR_INVALID_NUMBER_BINARY]              = { "invalid binary number", PM_ERROR_LEVEL_FATAL },