diff --git a/include/fkYAML/detail/input/lexical_analyzer.hpp b/include/fkYAML/detail/input/lexical_analyzer.hpp
index ecae08eb..7d94bd2b 100644
--- a/include/fkYAML/detail/input/lexical_analyzer.hpp
+++ b/include/fkYAML/detail/input/lexical_analyzer.hpp
@@ -396,6 +396,16 @@ class lexical_analyzer {
     /// @brief Skip until a newline code or a null character is found.
     void scan_comment() {
         FK_YAML_ASSERT(*m_cur_itr == '#');
+        if FK_YAML_LIKELY (m_cur_itr != m_begin_itr) {
+            switch (*(m_cur_itr - 1)) {
+            case ' ':
+            case '\t':
+            case '\n':
+                break;
+            default:
+                emit_error("Comment must not begin right after non-break characters");
+            }
+        }
         skip_until_line_end();
     }
 
diff --git a/single_include/fkYAML/node.hpp b/single_include/fkYAML/node.hpp
index 30dcf0bf..784953f3 100644
--- a/single_include/fkYAML/node.hpp
+++ b/single_include/fkYAML/node.hpp
@@ -3698,6 +3698,16 @@ class lexical_analyzer {
     /// @brief Skip until a newline code or a null character is found.
     void scan_comment() {
         FK_YAML_ASSERT(*m_cur_itr == '#');
+        if FK_YAML_LIKELY (m_cur_itr != m_begin_itr) {
+            switch (*(m_cur_itr - 1)) {
+            case ' ':
+            case '\t':
+            case '\n':
+                break;
+            default:
+                emit_error("Comment must not begin right after non-break characters");
+            }
+        }
         skip_until_line_end();
     }
 
diff --git a/tests/unit_test/test_lexical_analyzer_class.cpp b/tests/unit_test/test_lexical_analyzer_class.cpp
index b8273ee3..837b49a1 100644
--- a/tests/unit_test/test_lexical_analyzer_class.cpp
+++ b/tests/unit_test/test_lexical_analyzer_class.cpp
@@ -235,6 +235,31 @@ TEST_CASE("LexicalAnalyzer_EndOfDocuments") {
     REQUIRE(token.type == fkyaml::detail::lexical_token_t::END_OF_BUFFER);
 }
 
+TEST_CASE("LexicalAnalyzer_Comment") {
+    fkyaml::detail::lexical_token token;
+
+    SECTION("valid comments") {
+        auto input = GENERATE(
+            fkyaml::detail::str_view("# comment"),
+            fkyaml::detail::str_view(" # comment"),
+            fkyaml::detail::str_view("\t# comment\n"),
+            fkyaml::detail::str_view("\n# comment"));
+        fkyaml::detail::lexical_analyzer lexer(input);
+        REQUIRE_NOTHROW(token = lexer.get_next_token());
+        REQUIRE(token.type == fkyaml::detail::lexical_token_t::END_OF_BUFFER);
+    }
+
+    // regression test for https://github.com/fktn-k/fkYAML/pull/469
+    SECTION("invalid comments") {
+        fkyaml::detail::str_view input("\'foo\'#invalid");
+        fkyaml::detail::lexical_analyzer lexer(input);
+        REQUIRE_NOTHROW(token = lexer.get_next_token());
+        REQUIRE(token.type == fkyaml::detail::lexical_token_t::SINGLE_QUOTED_SCALAR);
+        REQUIRE(token.str == "foo");
+        REQUIRE_THROWS_AS(lexer.get_next_token(), fkyaml::parse_error);
+    }
+}
+
 TEST_CASE("LexicalAnalyzer_Colon") {
     fkyaml::detail::lexical_token token;