diff --git a/ext/mbstring/tests/utf8_mobile_encodings.phpt b/ext/mbstring/tests/utf8_mobile_encodings.phpt
index 918e897696d..21107ce5f08 100644
--- a/ext/mbstring/tests/utf8_mobile_encodings.phpt
+++ b/ext/mbstring/tests/utf8_mobile_encodings.phpt
@@ -31,6 +31,7 @@ $badUTF8 = array(
   // Multi-byte characters which end too soon and go to ASCII
   "\xDFA" => "\x00\x00\x00%\x00\x00\x00A",
   "\xEF\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
+  "\xF0\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
   "\xF0\xBF\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
 
   // Multi-byte characters which end too soon and go to another MB char
diff --git a/ext/mbstring/tests/utf_encodings.phpt b/ext/mbstring/tests/utf_encodings.phpt
index 490048058d9..92a9f4f1f56 100644
--- a/ext/mbstring/tests/utf_encodings.phpt
+++ b/ext/mbstring/tests/utf_encodings.phpt
@@ -778,6 +778,7 @@ $invalid = array(
   // Multi-byte characters which end too soon and go to ASCII
   "\xDFA" => "\x00\x00\x00%\x00\x00\x00A",
   "\xEF\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
+  "\xF0\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
   "\xF0\xBF\xBFA" => "\x00\x00\x00%\x00\x00\x00A",
 
   // Multi-byte characters which end too soon and go to another MB char
@@ -785,6 +786,11 @@ $invalid = array(
   "\xEF\xBF\xDF\xBF" => "\x00\x00\x00%\x00\x00\x07\xFF",
   "\xF0\xBF\xBF\xDF\xBF" => "\x00\x00\x00%\x00\x00\x07\xFF",
 
+  // Multi-byte characters which end too soon and go to a junk byte
+  // (Which isn't even valid to start a new character)
+  "\xF0\xBF\xBF\xFF" => "\x00\x00\x00%",
+  "\xF0\xBF\xFF" => "\x00\x00\x00%",
+
   // Continuation bytes which appear outside of a MB char
   "\x80" => "\x00\x00\x00%",
   "A\x80" => "\x00\x00\x00A\x00\x00\x00%",