diff --git a/src/calibre/utils/icu_calibre_utils.h b/src/calibre/utils/icu_calibre_utils.h
index c21578330c81..6de9e9e9c71d 100644
--- a/src/calibre/utils/icu_calibre_utils.h
+++ b/src/calibre/utils/icu_calibre_utils.h
@@ -22,11 +22,13 @@
 #include <unicode/unorm.h>
 #include <unicode/ubrk.h>
 
-#if PY_VERSION_HEX >= 0x03030000 
+#if PY_VERSION_HEX >= 0x03030000
 #error Not implemented for python >= 3.3
 #endif
 
 #define MIN(x, y) ((x)<(y)) ? (x) : (y)
+#define IS_HIGH_SURROGATE(x) (0xd800 <= x && x <= 0xdbff)
+#define IS_LOW_SURROGATE(x) (0xdc00 <= x && x <= 0xdfff)
 
 // Roundtripping will need to be implemented differently for python 3.3+ where strings are stored with variable widths
 
@@ -42,21 +44,29 @@ static UChar* python_to_icu(PyObject *obj, int32_t *osz, uint8_t do_check) {
         PyErr_SetString(PyExc_TypeError, "Not a unicode string");
         goto end;
     }
+    sz = PyUnicode_GET_SIZE(obj);
 
 #ifdef Py_UNICODE_WIDE
 // wide build (UCS 4)
-    sz = PyUnicode_GET_SIZE(obj);
     ans = (UChar*) calloc(2*(sz+1), sizeof(UChar)); // There can be no more than 2 UChars per character + ensure null termination
     if (ans == NULL) { PyErr_NoMemory(); goto end; }
-    u_strFromUTF32(ans, (int32_t)(2*(sz+1)), osz, (UChar32*)PyUnicode_AS_UNICODE(obj), (int32_t)sz, &status);
+    u_strFromUTF32WithSub(ans, (int32_t)(2*(sz+1)), osz, (UChar32*)PyUnicode_AS_UNICODE(obj), (int32_t)sz, 0xfffd, NULL, &status);
     if (U_FAILURE(status)) { PyErr_SetString(PyExc_ValueError, u_errorName(status)); free(ans); ans = NULL; goto end; }
 #else
 // narrow build (UTF-16)
-    sz = PyUnicode_GET_DATA_SIZE(obj);
-    ans = (UChar*) calloc(sz+2, 1);  // Ensure null termination
+    ans = (UChar*) malloc((sz + 1) * sizeof(UChar));
     if (ans == NULL) { PyErr_NoMemory(); goto end; }
-    memcpy(ans, PyUnicode_AS_UNICODE(obj), sz);
-    if (osz != NULL) *osz = (int32_t)PyUnicode_GET_SIZE(obj);
+    for (Py_ssize_t i = 0; i < sz; i++) {
+        UChar ch = PyUnicode_AS_UNICODE(obj)[i];
+        if (IS_HIGH_SURROGATE(ch)) {
+            if (i >= sz - 1 || !IS_LOW_SURROGATE(PyUnicode_AS_UNICODE(obj)[i+1])) ans[i] = 0xfffd;
+            else { ans[i] = ch; ans[i+1] = PyUnicode_AS_UNICODE(obj)[i+1]; i++; }
+        } else if (IS_LOW_SURROGATE(ch)) {
+            ans[i] = 0xfffd;
+        } else ans[i] = ch;
+    }
+    ans[sz] = 0; // Ensure null termination
+    if (osz != NULL) *osz = (int32_t)sz;
 #endif
 end:
     return ans;
@@ -104,5 +114,3 @@ static PyObject* icu_to_python(UChar *src, int32_t sz) {
 #endif
 }
 #endif
-
-
diff --git a/src/calibre/utils/icu_test.py b/src/calibre/utils/icu_test.py
index caa11d217a99..36cab51b4779 100644
--- a/src/calibre/utils/icu_test.py
+++ b/src/calibre/utils/icu_test.py
@@ -133,6 +133,8 @@ def test_roundtrip(self):
         ' Test roundtripping '
         for r in (u'xxx\0\u2219\U0001f431xxx', u'\0', u'', u'simple'):
             self.ae(r, icu._icu.roundtrip(r))
+        self.ae(icu._icu.roundtrip('\ud8e81'), '\ufffd1')
+        self.ae(icu._icu.roundtrip('\udc01\ud8e8'), '\ufffd\ufffd')
         for x, l in [('', 0), ('a', 1), ('\U0001f431', 1)]:
             self.ae(icu._icu.string_length(x), l)
         for x, l in [('', 0), ('a', 1), ('\U0001f431', 2)]:
@@ -218,6 +220,6 @@ def test_build():
     if not result.wasSuccessful():
         raise SystemExit(1)
 
+
 if __name__ == '__main__':
     run(verbosity=4)
-