diff --git a/prism/config.yml b/prism/config.yml
index 6e6e3d1e95..8ac65f2195 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -143,7 +143,8 @@ errors:
   - INVALID_NUMBER_DECIMAL
   - INVALID_NUMBER_HEXADECIMAL
   - INVALID_NUMBER_OCTAL
-  - INVALID_NUMBER_UNDERSCORE
+  - INVALID_NUMBER_UNDERSCORE_INNER
+  - INVALID_NUMBER_UNDERSCORE_TRAILING
   - INVALID_PERCENT
   - INVALID_PRINTABLE_CHARACTER
   - INVALID_RETRY_AFTER_ELSE
diff --git a/prism/prism.c b/prism/prism.c
index dae23842c6..56413361af 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -8558,10 +8558,11 @@ context_human(pm_context_t context) {
 /* Specific token lexers                                                      */
 /******************************************************************************/
 
-static void
-pm_strspn_number_validate(pm_parser_t *parser, const uint8_t *invalid) {
+static inline void
+pm_strspn_number_validate(pm_parser_t *parser, const uint8_t *string, size_t length, const uint8_t *invalid) {
     if (invalid != NULL) {
-        pm_parser_err(parser, invalid, invalid + 1, PM_ERR_INVALID_NUMBER_UNDERSCORE);
+        pm_diagnostic_id_t diag_id = (invalid == (string + length - 1)) ? PM_ERR_INVALID_NUMBER_UNDERSCORE_TRAILING : PM_ERR_INVALID_NUMBER_UNDERSCORE_INNER;
+        pm_parser_err(parser, invalid, invalid + 1, diag_id);
     }
 }
 
@@ -8569,7 +8570,7 @@ static size_t
 pm_strspn_binary_number_validate(pm_parser_t *parser, const uint8_t *string) {
     const uint8_t *invalid = NULL;
     size_t length = pm_strspn_binary_number(string, parser->end - string, &invalid);
-    pm_strspn_number_validate(parser, invalid);
+    pm_strspn_number_validate(parser, string, length, invalid);
     return length;
 }
 
@@ -8577,7 +8578,7 @@ static size_t
 pm_strspn_octal_number_validate(pm_parser_t *parser, const uint8_t *string) {
     const uint8_t *invalid = NULL;
     size_t length = pm_strspn_octal_number(string, parser->end - string, &invalid);
-    pm_strspn_number_validate(parser, invalid);
+    pm_strspn_number_validate(parser, string, length, invalid);
     return length;
 }
 
@@ -8585,7 +8586,7 @@ static size_t
 pm_strspn_decimal_number_validate(pm_parser_t *parser, const uint8_t *string) {
     const uint8_t *invalid = NULL;
     size_t length = pm_strspn_decimal_number(string, parser->end - string, &invalid);
-    pm_strspn_number_validate(parser, invalid);
+    pm_strspn_number_validate(parser, string, length, invalid);
     return length;
 }
 
@@ -8593,7 +8594,7 @@ static size_t
 pm_strspn_hexadecimal_number_validate(pm_parser_t *parser, const uint8_t *string) {
     const uint8_t *invalid = NULL;
     size_t length = pm_strspn_hexadecimal_number(string, parser->end - string, &invalid);
-    pm_strspn_number_validate(parser, invalid);
+    pm_strspn_number_validate(parser, string, length, invalid);
     return length;
 }
 
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index 02035fec24..38f806ea6d 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -222,7 +222,8 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_INVALID_NUMBER_DECIMAL]             = { "invalid decimal number; numeric literal without digits", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_NUMBER_HEXADECIMAL]         = { "invalid hexadecimal number; numeric literal without digits", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_NUMBER_OCTAL]               = { "invalid octal number; numeric literal without digits", PM_ERROR_LEVEL_SYNTAX },
-    [PM_ERR_INVALID_NUMBER_UNDERSCORE]          = { "invalid underscore placement in number", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_INVALID_NUMBER_UNDERSCORE_INNER]    = { "invalid underscore placement in number", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_INVALID_NUMBER_UNDERSCORE_TRAILING] = { "trailing '_' in number", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_CHARACTER]                  = { "invalid character 0x%X", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_MULTIBYTE_CHAR]             = { "invalid multibyte char (%s)", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_MULTIBYTE_CHARACTER]        = { "invalid multibyte character 0x%X", PM_ERROR_LEVEL_SYNTAX },
diff --git a/test/prism/errors_test.rb b/test/prism/errors_test.rb
index f989daa361..8a26663c07 100644
--- a/test/prism/errors_test.rb
+++ b/test/prism/errors_test.rb
@@ -1381,7 +1381,6 @@ module Prism
 
     def test_invalid_number_underscores
       error_messages = ["invalid underscore placement in number"]
-
       assert_error_messages "1__1", error_messages
       assert_error_messages "0b1__1", error_messages
       assert_error_messages "0o1__1", error_messages
@@ -1389,6 +1388,7 @@ module Prism
       assert_error_messages "0d1__1", error_messages
       assert_error_messages "0x1__1", error_messages
 
+      error_messages = ["trailing '_' in number"]
       assert_error_messages "1_1_", error_messages
       assert_error_messages "0b1_1_", error_messages
       assert_error_messages "0o1_1_", error_messages