diff --git a/include/boost/regex/v4/basic_regex_creator.hpp b/include/boost/regex/v4/basic_regex_creator.hpp
index fe971ed5..f3bc0061 100644
--- a/include/boost/regex/v4/basic_regex_creator.hpp
+++ b/include/boost/regex/v4/basic_regex_creator.hpp
@@ -1039,6 +1039,14 @@ int basic_regex_creator<charT, traits>::calculate_backstep(re_syntax_base* state
       case syntax_element_jump:
          state = static_cast<re_jump*>(state)->alt.p;
          continue;
+      case syntax_element_alt:
+         {
+            int r1 = calculate_backstep(state->next.p);
+            int r2 = calculate_backstep(static_cast<re_alt*>(state)->alt.p);
+            if((r1 < 0) || (r1 != r2))
+               return -1;
+            return result + r1;
+         }
       default:
          break;
       }
diff --git a/test/regress/test_perl_ex.cpp b/test/regress/test_perl_ex.cpp
index 27d5cee4..05abf22d 100644
--- a/test/regress/test_perl_ex.cpp
+++ b/test/regress/test_perl_ex.cpp
@@ -132,6 +132,8 @@ void test_conditionals()
    TEST_INVALID_REGEX("(?<!*|A)", perl);
    TEST_INVALID_REGEX("(?<=?|A)", perl);
    TEST_INVALID_REGEX("(?<=*|\\B)", perl);
+   TEST_INVALID_REGEX("(?<!a|bc)de", perl);
+   TEST_INVALID_REGEX("(?<=a|bc)de", perl);
 }
 
 void test_options()
@@ -278,8 +280,8 @@ void test_options2()
    TEST_REGEX_SEARCH("(?<=^[[:alpha:]]{4})(?:bar|cat)", perl, "aaaacat", match_default, make_array(4, 7, -2, -2));
    TEST_REGEX_SEARCH("(?<=^[[:alpha:]]{4})(?:bar|cat)", perl, "aaacat", match_default, make_array(-2, -2));
 
-   TEST_REGEX_SEARCH("(?<=ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "abxyZZ", match_default, make_array(4, 6, -2, -2));
-   TEST_REGEX_SEARCH("(?<=ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "abXyZZ", match_default, make_array(4, 6, -2, -2));
+   //TEST_REGEX_SEARCH("(?<=ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "abxyZZ", match_default, make_array(4, 6, -2, -2));
+   //TEST_REGEX_SEARCH("(?<=ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "abXyZZ", match_default, make_array(4, 6, -2, -2));
    TEST_REGEX_SEARCH("(?:ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "ZZZ", match_default, make_array(0, 3, -2, -2));
    TEST_REGEX_SEARCH("(?:ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "zZZ", match_default, make_array(0, 3, -2, -2));
    TEST_REGEX_SEARCH("(?:ab(?i)x(?-i)y|(?i)z|b)ZZ", perl, "bZZ", match_default, make_array(0, 3, -2, -2));