diff --git a/prism/config.yml b/prism/config.yml
index 5e6ee82ca4..4e85a6f34d 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -145,6 +145,7 @@ errors:
   - INVALID_MULTIBYTE_ESCAPE
   - INVALID_NUMBER_BINARY
   - INVALID_NUMBER_DECIMAL
+  - INVALID_NUMBER_FRACTION
   - INVALID_NUMBER_HEXADECIMAL
   - INVALID_NUMBER_OCTAL
   - INVALID_NUMBER_UNDERSCORE_INNER
diff --git a/prism/prism.c b/prism/prism.c
index 4f55dad954..44b4dc5ae5 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -8851,6 +8851,16 @@ lex_numeric_prefix(pm_parser_t *parser, bool* seen_e) {
         type = lex_optional_float_suffix(parser, seen_e);
     }
 
+    // At this point we have a completed number, but we want to provide the user
+    // with a good experience if they put an additional .xxx fractional
+    // component on the end, so we'll check for that here.
+    if (peek_offset(parser, 0) == '.' && pm_char_is_decimal_digit(peek_offset(parser, 1))) {
+        const uint8_t *fraction_start = parser->current.end;
+        const uint8_t *fraction_end = parser->current.end + 2;
+        fraction_end += pm_strspn_decimal_digit(fraction_end, parser->end - fraction_end);
+        pm_parser_err(parser, fraction_start, fraction_end, PM_ERR_INVALID_NUMBER_FRACTION);
+    }
+
     return type;
 }
 
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index ed3c61ec79..04b8af858b 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -224,6 +224,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_INVALID_LOCAL_VARIABLE_WRITE]       = { "identifier %.*s is not valid to set", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_NUMBER_BINARY]              = { "invalid binary number; numeric literal without digits", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_INVALID_NUMBER_DECIMAL]             = { "invalid decimal number; numeric literal without digits", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_INVALID_NUMBER_FRACTION]            = { "unexpected fraction part after numeric literal", 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_INNER]    = { "invalid underscore placement in number", PM_ERROR_LEVEL_SYNTAX },