diff --git a/include/boost/regex/v4/basic_regex_parser.hpp b/include/boost/regex/v4/basic_regex_parser.hpp
index fcf512c2..b2d99f09 100644
--- a/include/boost/regex/v4/basic_regex_parser.hpp
+++ b/include/boost/regex/v4/basic_regex_parser.hpp
@@ -784,6 +784,7 @@ bool basic_regex_parser<charT, traits>::parse_repeat(std::size_t low, std::size_
       case syntax_element_restart_continue:
       case syntax_element_jump:
       case syntax_element_startmark:
+      case syntax_element_backstep:
          // can't legally repeat any of the above:
          fail(regex_constants::error_badrepeat, m_position - m_base);
          return false;
@@ -1869,6 +1870,7 @@ bool basic_regex_parser<charT, traits>::parse_perl_extension()
    if(markid == -4)
    {
       re_syntax_base* b = this->getaddress(expected_alt_point);
+      // Make sure we have exactly one alternative following this state:
       if(b->type != syntax_element_alt)
       {
          re_alt* alt = static_cast<re_alt*>(this->insert_state(expected_alt_point, syntax_element_alt, sizeof(re_alt)));
@@ -1879,6 +1881,15 @@ bool basic_regex_parser<charT, traits>::parse_perl_extension()
          fail(regex_constants::error_bad_pattern, m_position - m_base);
          return false;
       }
+      // check for invalid repetition of next state:
+      b = this->getaddress(expected_alt_point);
+      b = this->getaddress(static_cast<re_alt*>(b)->next.i, b);
+      if((b->type != syntax_element_assert_backref)
+         && (b->type != syntax_element_startmark))
+      {
+         fail(regex_constants::error_badrepeat, m_position - m_base);
+         return false;
+      }
    }
    //
    // append closing parenthesis state:
diff --git a/test/regress/test_perl_ex.cpp b/test/regress/test_perl_ex.cpp
index 82a0517f..3bf104b7 100644
--- a/test/regress/test_perl_ex.cpp
+++ b/test/regress/test_perl_ex.cpp
@@ -121,6 +121,17 @@ void test_conditionals()
    TEST_INVALID_REGEX("(?:(a)|b)(?(?:", perl);
    TEST_INVALID_REGEX("(?:(a)|b)(?(?<", perl);
    TEST_INVALID_REGEX("(?:(a)|b)(?(?<a", perl);
+
+   TEST_INVALID_REGEX("(?(?!#?)+)", perl);
+   TEST_INVALID_REGEX("(?(?=:-){0})", perl);
+   TEST_INVALID_REGEX("(?(123){1})", perl);
+   TEST_INVALID_REGEX("(?(?<=A)*)", perl);
+   TEST_INVALID_REGEX("(?(?<=A)+)", perl);
+
+   TEST_INVALID_REGEX("(?<!*|^)", perl);
+   TEST_INVALID_REGEX("(?<!*|A)", perl);
+   TEST_INVALID_REGEX("(?<=?|A)", perl);
+   TEST_INVALID_REGEX("(?<=*|\B)", perl);
 }
 
 void test_options()