diff --git a/expat/lib/internal.h b/expat/lib/internal.h
index 8eb7190..94cb98e 100644
--- a/expat/lib/internal.h
+++ b/expat/lib/internal.h
@@ -79,3 +79,17 @@
 #  define UNUSED_P(p) UNUSED_ ## p
 # endif
 #endif
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+void
+align_limit_to_full_utf8_characters(const char * from, const char ** fromLimRef);
+
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/expat/lib/xmltok.c b/expat/lib/xmltok.c
index 0e68844..4195279 100644
--- a/expat/lib/xmltok.c
+++ b/expat/lib/xmltok.c
@@ -329,6 +329,41 @@
   UTF8_cval4 = 0xf0
 };
 
+void
+align_limit_to_full_utf8_characters(const char * from, const char ** fromLimRef)
+{
+  const char * fromLim = *fromLimRef;
+  size_t walked = 0;
+  for (; fromLim > from; fromLim--, walked++) {
+    const unsigned char prev = (unsigned char)fromLim[-1];
+    if ((prev & 0xf8u) == 0xf0u) { /* 4-byte character, lead by 0b11110xxx byte */
+      if (walked + 1 >= 4) {
+        fromLim += 4 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0xf0u) == 0xe0u) { /* 3-byte character, lead by 0b1110xxxx byte */
+      if (walked + 1 >= 3) {
+        fromLim += 3 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0xe0u) == 0xc0u) { /* 2-byte character, lead by 0b110xxxxx byte */
+      if (walked + 1 >= 2) {
+        fromLim += 2 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0x80u) == 0x00u) { /* 1-byte character, matching 0b0xxxxxxx */
+      break;
+    }
+  }
+  *fromLimRef = fromLim;
+}
+
 static enum XML_Convert_Result PTRCALL
 utf8_toUtf8(const ENCODING *UNUSED_P(enc),
             const char **fromP, const char *fromLim,
@@ -340,9 +375,8 @@
   if (fromLim - *fromP > toLim - *toP) {
     /* Avoid copying partial characters. */
     res = XML_CONVERT_OUTPUT_EXHAUSTED;
-    for (fromLim = *fromP + (toLim - *toP); fromLim > *fromP; fromLim--)
-      if (((unsigned char)fromLim[-1] & 0xc0) != 0x80)
-        break;
+    fromLim = *fromP + (toLim - *toP);
+    align_limit_to_full_utf8_characters(*fromP, &fromLim);
   }
   for (to = *toP, from = *fromP; (from < fromLim) && (to < toLim); from++, to++)
     *to = *from;
diff --git a/expat/tests/runtests.c b/expat/tests/runtests.c
index 45adfa5..c0cdea9 100644
--- a/expat/tests/runtests.c
+++ b/expat/tests/runtests.c
@@ -13,6 +13,10 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdint.h>
+#include <stddef.h>  /* ptrdiff_t */
+#ifndef __cplusplus
+# include <stdbool.h>
+#endif
 
 #include "expat.h"
 #include "chardata.h"
@@ -367,6 +371,68 @@
 }
 END_TEST
 
+
+/* Examples, not masks: */
+#define UTF8_LEAD_1  "\x7f"  /* 0b01111111 */
+#define UTF8_LEAD_2  "\xdf"  /* 0b11011111 */
+#define UTF8_LEAD_3  "\xef"  /* 0b11101111 */
+#define UTF8_LEAD_4  "\xf7"  /* 0b11110111 */
+#define UTF8_FOLLOW  "\xbf"  /* 0b10111111 */
+
+START_TEST(test_utf8_auto_align)
+{
+    struct TestCase {
+        ptrdiff_t expectedMovementInChars;
+        const char * input;
+    };
+
+    struct TestCase cases[] = {
+        {00, ""},
+
+        {00, UTF8_LEAD_1},
+
+        {-1, UTF8_LEAD_2},
+        {00, UTF8_LEAD_2 UTF8_FOLLOW},
+
+        {-1, UTF8_LEAD_3},
+        {-2, UTF8_LEAD_3 UTF8_FOLLOW},
+        {00, UTF8_LEAD_3 UTF8_FOLLOW UTF8_FOLLOW},
+
+        {-1, UTF8_LEAD_4},
+        {-2, UTF8_LEAD_4 UTF8_FOLLOW},
+        {-3, UTF8_LEAD_4 UTF8_FOLLOW UTF8_FOLLOW},
+        {00, UTF8_LEAD_4 UTF8_FOLLOW UTF8_FOLLOW UTF8_FOLLOW},
+    };
+
+    size_t i = 0;
+    bool success = true;
+    for (; i < sizeof(cases) / sizeof(*cases); i++) {
+        const char * fromLim = cases[i].input + strlen(cases[i].input);
+        const char * const fromLimInitially = fromLim;
+        ptrdiff_t actualMovementInChars;
+
+        align_limit_to_full_utf8_characters(cases[i].input, &fromLim);
+
+        actualMovementInChars = (fromLim - fromLimInitially);
+        if (actualMovementInChars != cases[i].expectedMovementInChars) {
+            size_t j = 0;
+            success = false;
+            printf("[-] UTF-8 case %2lu: Expected movement by %2ld chars"
+                    ", actually moved by %2ld chars: \"",
+                    i + 1, cases[i].expectedMovementInChars, actualMovementInChars);
+            for (; j < strlen(cases[i].input); j++) {
+                printf("\\x%02x", (unsigned char)cases[i].input[j]);
+            }
+            printf("\"\n");
+        }
+    }
+
+    if (! success) {
+        fail("UTF-8 auto-alignment is not bullet-proof\n");
+    }
+}
+END_TEST
+
 START_TEST(test_utf16)
 {
     /* <?xml version="1.0" encoding="UTF-16"?>
@@ -1543,6 +1609,7 @@
     tcase_add_test(tc_basic, test_bom_utf16_be);
     tcase_add_test(tc_basic, test_bom_utf16_le);
     tcase_add_test(tc_basic, test_illegal_utf8);
+    tcase_add_test(tc_basic, test_utf8_auto_align);
     tcase_add_test(tc_basic, test_utf16);
     tcase_add_test(tc_basic, test_utf16_le_epilog_newline);
     tcase_add_test(tc_basic, test_latin1_umlauts);