diff --git a/i18nutil/source/utility/unicode.cxx b/i18nutil/source/utility/unicode.cxx
index b0e1cd4d85ef..ae40fa421c0a 100644
--- a/i18nutil/source/utility/unicode.cxx
+++ b/i18nutil/source/utility/unicode.cxx
@@ -1068,7 +1068,7 @@ OUString unicode::formatPercent(double dNumber,
     return aRet;
 }
 
-bool ToggleUnicodeCodepoint::AllowMoreInput(sal_Unicode uChar)
+bool ToggleUnicodeCodepoint::AllowMoreInput(sal_uInt32 uChar)
 {
     //arbitrarily chosen maximum length allowed - normal max usage would be around 30.
     if( maInput.getLength() > 255 )
@@ -1092,12 +1092,20 @@ bool ToggleUnicodeCodepoint::AllowMoreInput(sal_Unicode uChar)
 
             if( rtl::isLowSurrogate(uChar) && maUtf16.isEmpty() && maInput.isEmpty()  )
             {
-                maUtf16.append(uChar);
+                maUtf16.append(sal_Unicode(uChar));
                 return true;
             }
             if( rtl::isHighSurrogate(uChar) && maInput.isEmpty() )
-                maUtf16.insert(0, uChar );
-            //end of hex strings, or unexpected order of high/low, so don't accept more
+                maUtf16.insert(0, sal_Unicode(uChar));
+            if (maUtf16.getLength() == 2)
+            {
+                assert(rtl::isHighSurrogate(maUtf16[0]) && rtl::isLowSurrogate(maUtf16[1]));
+                // The resulting codepoint may itself be combining, so may allow more
+                sal_uInt32 nUCS4 = rtl::combineSurrogates(maUtf16[0], maUtf16[1]);
+                maUtf16.setLength(0);
+                return AllowMoreInput(nUCS4);
+            }
+            // unexpected order of high/low, so don't accept more
             if( !maUtf16.isEmpty() )
                 maInput.append(maUtf16);
             if( !maCombining.isEmpty() )
@@ -1122,7 +1130,7 @@ bool ToggleUnicodeCodepoint::AllowMoreInput(sal_Unicode uChar)
                 mbAllowMoreChars = false;
                 return false;
             }
-            maCombining.insert(0, uChar);
+            maCombining.insertUtf32(0, uChar);
             break;
 
         default:
@@ -1138,7 +1146,7 @@ bool ToggleUnicodeCodepoint::AllowMoreInput(sal_Unicode uChar)
 
             if( !maCombining.isEmpty() )
             {
-                maCombining.insert(0, uChar);
+                maCombining.insertUtf32(0, uChar);
                 maInput = maCombining;
                 mbAllowMoreChars = false;
                 return false;
diff --git a/include/i18nutil/unicode.hxx b/include/i18nutil/unicode.hxx
index be08595e0b10..b7722fd77196 100644
--- a/include/i18nutil/unicode.hxx
+++ b/include/i18nutil/unicode.hxx
@@ -102,11 +102,11 @@ private:
 
 public:
     /**
-    Build an input string of valid UTF16 units to toggle.
+    Build an input string of valid UTF16/UCS4 units to toggle.
         -do not call the other functions until the input process is complete
         -build string from Right to Left.  (Start from the character to the left of the cursor: move left.)
     */
-    bool AllowMoreInput(sal_Unicode uChar);
+    bool AllowMoreInput(sal_uInt32 uChar);
 
     /**
     Validates (and potentially modifies) the input string.
diff --git a/sw/qa/extras/uiwriter/uiwriter7.cxx b/sw/qa/extras/uiwriter/uiwriter7.cxx
index 4b3f1c9c533f..18c7fefd3248 100644
--- a/sw/qa/extras/uiwriter/uiwriter7.cxx
+++ b/sw/qa/extras/uiwriter/uiwriter7.cxx
@@ -2405,8 +2405,8 @@ CPPUNIT_TEST_FIXTURE(SwUiWriterTest7, testUnicodeNotationToggle)
     sDocString = pWrtShell->GetCursor()->GetPointNode().GetTextNode()->GetText();
     CPPUNIT_ASSERT_EQUAL(sOriginalDocString, sDocString);
 
-    constexpr OUString sWithCombiningSMPName = u"xyzU+e0101"_ustr;
-    constexpr OUString sWithCombiningSMP = u"xyz\U000e0101"_ustr;
+    constexpr OUString sWithCombiningSMPName = u"xyzU+4faeU+e0101"_ustr;
+    constexpr OUString sWithCombiningSMP = u"xyz\U00004fae\U000e0101"_ustr;
     pWrtShell->SplitNode();
     pWrtShell->Insert2(sWithCombiningSMPName);
     dispatchCommand(mxComponent, u".uno:UnicodeNotationToggle"_ustr, aPropertyValues);
@@ -2416,9 +2416,13 @@ CPPUNIT_TEST_FIXTURE(SwUiWriterTest7, testUnicodeNotationToggle)
     dispatchCommand(mxComponent, u".uno:UnicodeNotationToggle"_ustr, aPropertyValues);
     sDocString = pWrtShell->GetCursor()->GetPointNode().GetTextNode()->GetText();
     // Before tdf#162656 fix, this failed with
-    // - Expected: xyzU+e0101
-    // - Actual  : xyU+e0101
+    // - Expected: xyzU+4faeU+e0101
+    // - Actual  : xyxU+e0101
     // i.e., one codepoint to the left of the combining codepoint was removed
+    // Before tdf#162657 fix, this failed with
+    // - Expected: xyzU+4faeU+e0101
+    // - Actual  : xyz侮U+e0101
+    // i.e., one codepoint to the left of the combining codepoint was not converted
     CPPUNIT_ASSERT_EQUAL(sWithCombiningSMPName, sDocString);
 }