diff --git a/prism/config.yml b/prism/config.yml
index 4e85a6f34d..9268effce7 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -290,6 +290,7 @@ warnings:
   - KEYWORD_EOL
   - LITERAL_IN_CONDITION_DEFAULT
   - LITERAL_IN_CONDITION_VERBOSE
+  - SHAREABLE_CONSTANT_VALUE_LINE
   - SHEBANG_CARRIAGE_RETURN
   - UNEXPECTED_CARRIAGE_RETURN
   - UNREACHABLE_STATEMENT
diff --git a/prism/prism.c b/prism/prism.c
index 44b4dc5ae5..12bbf1b597 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -8394,7 +8394,12 @@ parser_lex_magic_comment(pm_parser_t *parser, bool semantic_token_seen) {
         // If we have hit a ractor pragma, attempt to lex that.
         uint32_t value_length = (uint32_t) (value_end - value_start);
         if (key_length == 24 && pm_strncasecmp(key_source, (const uint8_t *) "shareable_constant_value", 24) == 0) {
-            if (value_length == 4 && pm_strncasecmp(value_start, (const uint8_t *) "none", 4) == 0) {
+            const uint8_t *cursor = parser->current.start;
+            while ((cursor > parser->start) && ((cursor[-1] == ' ') || (cursor[-1] == '\t'))) cursor--;
+
+            if (!((cursor == parser->start) || (cursor[-1] == '\n'))) {
+                pm_parser_warn_token(parser, &parser->current, PM_WARN_SHAREABLE_CONSTANT_VALUE_LINE);
+            } else if (value_length == 4 && pm_strncasecmp(value_start, (const uint8_t *) "none", 4) == 0) {
                 pm_parser_scope_shareable_constant_set(parser, PM_SCOPE_SHAREABLE_CONSTANT_NONE);
             } else if (value_length == 7 && pm_strncasecmp(value_start, (const uint8_t *) "literal", 7) == 0) {
                 pm_parser_scope_shareable_constant_set(parser, PM_SCOPE_SHAREABLE_CONSTANT_LITERAL);
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index 04b8af858b..ba17cf8306 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -373,6 +373,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_WARN_KEYWORD_EOL]                       = { "`%.*s` at the end of line without an expression", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_LITERAL_IN_CONDITION_DEFAULT]      = { "%sliteral in %s", PM_WARNING_LEVEL_DEFAULT },
     [PM_WARN_LITERAL_IN_CONDITION_VERBOSE]      = { "%sliteral in %s", PM_WARNING_LEVEL_VERBOSE },
+    [PM_WARN_SHAREABLE_CONSTANT_VALUE_LINE]     = { "'shareable_constant_value' is ignored unless in comment-only line", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_SHEBANG_CARRIAGE_RETURN]           = { "shebang line ending with \\r may cause problems", PM_WARNING_LEVEL_DEFAULT },
     [PM_WARN_UNEXPECTED_CARRIAGE_RETURN]        = { "encountered \\r in middle of line, treated as a mere space", PM_WARNING_LEVEL_DEFAULT },
     [PM_WARN_UNREACHABLE_STATEMENT]             = { "statement not reached", PM_WARNING_LEVEL_VERBOSE },
diff --git a/test/prism/warnings_test.rb b/test/prism/warnings_test.rb
index d01db01a0e..b138a3cb43 100644
--- a/test/prism/warnings_test.rb
+++ b/test/prism/warnings_test.rb
@@ -64,6 +64,15 @@ module Prism
       assert_warning("if true\nelsif\nfalse; end", "end of line")
     end
 
+    def test_shareable_constant_value
+      assert_warning("foo # shareable_constant_value: none", "ignored")
+      assert_warning("\v  # shareable_constant_value: none", "ignored")
+
+      refute_warning("# shareable_constant_value: none")
+      refute_warning("    # shareable_constant_value: none")
+      refute_warning("\t\t# shareable_constant_value: none")
+    end
+
     def test_string_in_predicate
       assert_warning("if 'foo'; end", "string")
       assert_warning("if \"\#{foo}\"; end", "string")