diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index 389b1dc484..9a30a57e3b 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -184,7 +184,8 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_EXPECT_FOR_DELIMITER]               = { "unexpected %s; expected a 'do', newline, or ';' after the 'for' loop collection", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_IDENT_REQ_PARAMETER]         = { "expected an identifier for the required parameter", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_IN_DELIMITER]                = { "expected a delimiter after the patterns of an `in` clause", PM_ERROR_LEVEL_SYNTAX },
-    [PM_ERR_EXPECT_LPAREN_AFTER_NOT]            = { "expected a `(` after `not`", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPECT_LPAREN_AFTER_NOT_LPAREN]     = { "expected a `(` immediately after `not`", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_EXPECT_LPAREN_AFTER_NOT_OTHER]      = { "expected a `(` after `not`", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_LPAREN_REQ_PARAMETER]        = { "expected a `(` to start a required parameter", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_MESSAGE]                     = { "unexpected %s; expecting a message to send to the receiver", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_EXPECT_RBRACKET]                    = { "expected a matching `]`", PM_ERROR_LEVEL_SYNTAX },
diff --git a/test/prism/errors/command_calls_31.txt b/test/prism/errors/command_calls_31.txt
index 72d5fc588f..e662b25444 100644
--- a/test/prism/errors/command_calls_31.txt
+++ b/test/prism/errors/command_calls_31.txt
@@ -7,6 +7,11 @@ true || not true
             ^~~~ unexpected 'true', expecting end-of-input
 
 true && not (true)
-            ^ expected a `(` after `not`
+           ^ expected a `(` immediately after `not`
             ^ unexpected '(', expecting end-of-input
 
+true && not
+true
+^~~~ expected a `(` after `not`
+^~~~ unexpected 'true', expecting end-of-input
+