diff --git a/src/common/strconv.cpp b/src/common/strconv.cpp
index a433128011..6c671f0d9f 100644
--- a/src/common/strconv.cpp
+++ b/src/common/strconv.cpp
@@ -1272,6 +1272,14 @@ size_t wxMBConvUTF8::ToWChar(wchar_t *buf, size_t n,
                 wxUint32 res = cc & (0x3f >> cnt);
                 while (cnt--)
                 {
+                    if (!isNulTerminated && !srcLen)
+                    {
+                        // invalid UTF-8 sequence ending before the end of code
+                        // point.
+                        invalid = true;
+                        break;
+                    }
+
                     cc = *psz;
                     if ((cc & 0xC0) != 0x80)
                     {
@@ -1281,6 +1289,8 @@ size_t wxMBConvUTF8::ToWChar(wchar_t *buf, size_t n,
                     }
 
                     psz++;
+                    if (!isNulTerminated)
+                        srcLen--;
                     res = (res << 6) | (cc & 0x3f);
                 }
 
diff --git a/tests/strings/unicode.cpp b/tests/strings/unicode.cpp
index 29b7777a2a..2fd2ad3a6a 100644
--- a/tests/strings/unicode.cpp
+++ b/tests/strings/unicode.cpp
@@ -352,6 +352,13 @@ void UnicodeTestCase::ConversionUTF8()
         d.Test(n, conv);
         d.Test(n, wxConvUTF8);
     }
+
+    static const char* const u25a6 = "\xe2\x96\xa6";
+    wxMBConvUTF8 c(wxMBConvUTF8::MAP_INVALID_UTF8_TO_OCTAL);
+    CPPUNIT_ASSERT_EQUAL( 2, c.ToWChar(NULL, 0, u25a6, wxNO_LEN) );
+    CPPUNIT_ASSERT_EQUAL( 0, c.ToWChar(NULL, 0, u25a6, 0) );
+    CPPUNIT_ASSERT_EQUAL( 1, c.ToWChar(NULL, 0, u25a6, 3) );
+    CPPUNIT_ASSERT_EQUAL( 2, c.ToWChar(NULL, 0, u25a6, 4) );
 }
 
 void UnicodeTestCase::ConversionUTF16()