diff --git a/bstring/bstraux.c b/bstring/bstraux.c
index 18d33c9..92d57fe 100644
--- a/bstring/bstraux.c
+++ b/bstring/bstraux.c
@@ -909,6 +909,25 @@ bYDecode(const bstring src)
 	return out;
 }
 
+/*  int bSGMLEncode (bstring b)
+ *
+ *  Change the string into a version that is quotable in SGML (HTML, XML).
+ */
+int
+bSGMLEncode(bstring b)
+{
+static struct tagbstring fr[4][2] = {
+	{ bsStatic("&"),  bsStatic("&")  },
+	{ bsStatic("\""), bsStatic(""") },
+	{ bsStatic("<"),  bsStatic("&lt;")   },
+	{ bsStatic(">"),  bsStatic("&gt;")   } };
+	for (int i = 0; i < 4; i++) {
+		int ret = bfindreplace(b, &fr[i][0], &fr[i][1], 0);
+		if (0 > ret) return ret;
+	}
+	return 0;
+}
+
 bstring
 bStrfTime(const char * fmt, const struct tm * timeptr)
 {
diff --git a/bstring/bstraux.h b/bstring/bstraux.h
index 12e6125..ac9a2ba 100644
--- a/bstring/bstraux.h
+++ b/bstring/bstraux.h
@@ -322,6 +322,16 @@ bYEncode(const bstring src);
 BSTR_PUBLIC bstring
 bYDecode(const bstring src);
 
+/**
+ * Change the string into a version that is quotable in SGML (HTML, XML).
+ * Replaces &, ", <, > with their SGML entity equivalents.
+ *
+ * @param b the bstring to encode in-place
+ * @return BSTR_OK on success, BSTR_ERR on error
+ */
+BSTR_PUBLIC int
+bSGMLEncode(bstring b);
+
 /* Writable stream */
 typedef int
 (*bNwrite)(const void *buf, size_t elsize, size_t nelem, void *parm);
diff --git a/tests/testaux.c b/tests/testaux.c
index 6cc6983..ff80d96 100644
--- a/tests/testaux.c
+++ b/tests/testaux.c
@@ -483,6 +483,33 @@ START_TEST(core_013)
 }
 END_TEST
 
+START_TEST(core_014)
+{
+	bstring b;
+
+	/* All four entities: &, ", <, > */
+	b = bfromcstr("<\"Hello, you, me, & world\">");
+	ck_assert_int_eq(bSGMLEncode(b), BSTR_OK);
+	ck_assert_int_eq(biseqcstr(b, "&lt;&quot;Hello, you, me, &amp; world&quot;&gt;"), 1);
+	bdestroy(b);
+
+	/* No special characters — string should be unchanged */
+	b = bfromcstr("Hello, world");
+	ck_assert_int_eq(bSGMLEncode(b), BSTR_OK);
+	ck_assert_int_eq(biseqcstr(b, "Hello, world"), 1);
+	bdestroy(b);
+
+	/* Empty string */
+	b = bfromcstr("");
+	ck_assert_int_eq(bSGMLEncode(b), BSTR_OK);
+	ck_assert_int_eq(biseqcstr(b, ""), 1);
+	bdestroy(b);
+
+	/* NULL input */
+	ck_assert_int_eq(bSGMLEncode(NULL), BSTR_ERR);
+}
+END_TEST
+
 int
 main(void)
 {
@@ -504,6 +531,7 @@ main(void)
 	tcase_add_test(core, core_011);
 	tcase_add_test(core, core_012);
 	tcase_add_test(core, core_013);
+	tcase_add_test(core, core_014);
 	suite_add_tcase(suite, core);
 	/* Run tests */
 	SRunner *runner = srunner_create(suite);