Index: /trunk/boost/regex/v4/basic_regex_parser.hpp
===================================================================
--- /trunk/boost/regex/v4/basic_regex_parser.hpp (revision 38864)
+++ /trunk/boost/regex/v4/basic_regex_parser.hpp (revision 42674)
@@ -785,4 +785,5 @@
       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);
@@ -1870,4 +1871,5 @@
    {
       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)
       {
@@ -1878,4 +1880,13 @@
       {
          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;
       }
Index: /trunk/libs/regex/test/regress/test_perl_ex.cpp
===================================================================
--- /trunk/libs/regex/test/regress/test_perl_ex.cpp (revision 30980)
+++ /trunk/libs/regex/test/regress/test_perl_ex.cpp (revision 42674)
@@ -122,4 +122,15 @@
    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);
 }