diff --git a/python/ql/src/semmle/python/regex.qll b/python/ql/src/semmle/python/regex.qll
index 0636c485f06..da232c0fdf1 100644
--- a/python/ql/src/semmle/python/regex.qll
+++ b/python/ql/src/semmle/python/regex.qll
@@ -565,10 +565,8 @@ abstract class RegexString extends Expr {
         this.sequenceOrQualified(start, end) and not this.isOptionDivider(start-1) and
         item_start = start
         or
-        exists(int endp1 | end = endp1-1 |
-            start = end and not this.item_end(start) and this.isOptionDivider(endp1) and
-            item_start = start
-        )
+        start = end and not this.item_end(start) and this.isOptionDivider(end) and
+        item_start = start
         or
         exists(int mid |
             this.subalternation(start, mid, _) and
diff --git a/python/ql/test/library-tests/regex/Alternation.expected b/python/ql/test/library-tests/regex/Alternation.expected
index cba6212a273..2fe6572074e 100644
--- a/python/ql/test/library-tests/regex/Alternation.expected
+++ b/python/ql/test/library-tests/regex/Alternation.expected
@@ -1,5 +1,7 @@
 | (?:(?:\n\r?)\|^)( *)\\S | 3 | 12 | (?:\n\r?)\|^ | 3 | 10 | (?:\n\r?) |
 | (?:(?:\n\r?)\|^)( *)\\S | 3 | 12 | (?:\n\r?)\|^ | 11 | 12 | ^ |
+| (?:(?P<n1>^(?:\|x))) | 14 | 16 | \|x | 14 | 14 |  |
+| (?:(?P<n1>^(?:\|x))) | 14 | 16 | \|x | 15 | 16 | x |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 3 | 9 | [^%]\|^ | 3 | 7 | [^%] |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 3 | 9 | [^%]\|^ | 8 | 9 | ^ |
 | (?P<name>[\\w]+)\| | 0 | 16 | (?P<name>[\\w]+)\| | 0 | 15 | (?P<name>[\\w]+) |
@@ -8,10 +10,13 @@
 | (\\033\|~{) | 1 | 8 | \\033\|~{ | 6 | 8 | ~{ |
 | \\\|\\[\\][123]\|\\{\\} | 0 | 16 | \\\|\\[\\][123]\|\\{\\} | 0 | 11 | \\\|\\[\\][123] |
 | \\\|\\[\\][123]\|\\{\\} | 0 | 16 | \\\|\\[\\][123]\|\\{\\} | 12 | 16 | \\{\\} |
+| \|x | 0 | 2 | \|x | 0 | 0 |  |
+| \|x | 0 | 2 | \|x | 1 | 2 | x |
 | ^(^y\|^z)(u$\|v$)$ | 2 | 7 | ^y\|^z | 2 | 4 | ^y |
 | ^(^y\|^z)(u$\|v$)$ | 2 | 7 | ^y\|^z | 5 | 7 | ^z |
 | ^(^y\|^z)(u$\|v$)$ | 9 | 14 | u$\|v$ | 9 | 11 | u$ |
 | ^(^y\|^z)(u$\|v$)$ | 9 | 14 | u$\|v$ | 12 | 14 | v$ |
-| x\|(?<!\\w)l | 0 | 10 | x\|(?<!\\w)l | 0 | 0 |  |
+| x\| | 0 | 2 | x\| | 0 | 1 | x |
+| x\| | 0 | 2 | x\| | 2 | 2 |  |
 | x\|(?<!\\w)l | 0 | 10 | x\|(?<!\\w)l | 0 | 1 | x |
 | x\|(?<!\\w)l | 0 | 10 | x\|(?<!\\w)l | 2 | 10 | (?<!\\w)l |
\ No newline at end of file
diff --git a/python/ql/test/library-tests/regex/Characters.expected b/python/ql/test/library-tests/regex/Characters.expected
index 9579d2c8e42..f490522dc4c 100644
--- a/python/ql/test/library-tests/regex/Characters.expected
+++ b/python/ql/test/library-tests/regex/Characters.expected
@@ -25,6 +25,8 @@
 | (?:(?:\n\r?)\|^)( *)\\S | 11 | 12 |
 | (?:(?:\n\r?)\|^)( *)\\S | 14 | 15 |
 | (?:(?:\n\r?)\|^)( *)\\S | 17 | 19 |
+| (?:(?P<n1>^(?:\|x))) | 10 | 11 |
+| (?:(?P<n1>^(?:\|x))) | 15 | 16 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 5 | 6 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 8 | 9 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 11 | 12 |
@@ -62,6 +64,7 @@
 | \\\|\\[\\][123]\|\\{\\} | 9 | 10 |
 | \\\|\\[\\][123]\|\\{\\} | 12 | 14 |
 | \\\|\\[\\][123]\|\\{\\} | 14 | 16 |
+| \|x | 1 | 2 |
 | ^(^y\|^z)(u$\|v$)$ | 0 | 1 |
 | ^(^y\|^z)(u$\|v$)$ | 2 | 3 |
 | ^(^y\|^z)(u$\|v$)$ | 3 | 4 |
@@ -110,6 +113,7 @@
 | ax{,3} | 3 | 4 |
 | ax{,3} | 4 | 5 |
 | ax{,3} | 5 | 6 |
+| x\| | 0 | 1 |
 | x\|(?<!\\w)l | 0 | 1 |
 | x\|(?<!\\w)l | 6 | 8 |
 | x\|(?<!\\w)l | 9 | 10 |
diff --git a/python/ql/test/library-tests/regex/FirstLast.expected b/python/ql/test/library-tests/regex/FirstLast.expected
index abc53cfb6e8..52ec6df203a 100644
--- a/python/ql/test/library-tests/regex/FirstLast.expected
+++ b/python/ql/test/library-tests/regex/FirstLast.expected
@@ -10,6 +10,9 @@
 | (?:(?:\n\r?)\|^)( *)\\S | first | 6 | 7 |
 | (?:(?:\n\r?)\|^)( *)\\S | first | 11 | 12 |
 | (?:(?:\n\r?)\|^)( *)\\S | last | 17 | 19 |
+| (?:(?P<n1>^(?:\|x))) | first | 10 | 11 |
+| (?:(?P<n1>^(?:\|x))) | first | 15 | 16 |
+| (?:(?P<n1>^(?:\|x))) | last | 15 | 16 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | first | 0 | 11 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | first | 3 | 7 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | first | 8 | 9 |
@@ -46,6 +49,8 @@
 | \\\|\\[\\][123]\|\\{\\} | first | 12 | 14 |
 | \\\|\\[\\][123]\|\\{\\} | last | 6 | 11 |
 | \\\|\\[\\][123]\|\\{\\} | last | 14 | 16 |
+| \|x | first | 1 | 2 |
+| \|x | last | 1 | 2 |
 | ^(^y\|^z)(u$\|v$)$ | first | 0 | 1 |
 | ^(^y\|^z)(u$\|v$)$ | first | 2 | 3 |
 | ^(^y\|^z)(u$\|v$)$ | first | 3 | 4 |
@@ -82,6 +87,8 @@
 | ax{,3} | last | 1 | 2 |
 | ax{,3} | last | 1 | 6 |
 | ax{,3} | last | 5 | 6 |
+| x\| | first | 0 | 1 |
+| x\| | last | 0 | 1 |
 | x\|(?<!\\w)l | first | 0 | 1 |
 | x\|(?<!\\w)l | first | 6 | 8 |
 | x\|(?<!\\w)l | first | 9 | 10 |
diff --git a/python/ql/test/library-tests/regex/GroupContents.expected b/python/ql/test/library-tests/regex/GroupContents.expected
index 6deb2471da2..70857930302 100644
--- a/python/ql/test/library-tests/regex/GroupContents.expected
+++ b/python/ql/test/library-tests/regex/GroupContents.expected
@@ -2,6 +2,9 @@
 | (?:(?:\n\r?)\|^)( *)\\S | 0 | 13 | (?:(?:\n\r?)\|^) | 3 | 12 | (?:\n\r?)\|^ |
 | (?:(?:\n\r?)\|^)( *)\\S | 3 | 10 | (?:\n\r?) | 6 | 9 | \n\r? |
 | (?:(?:\n\r?)\|^)( *)\\S | 13 | 17 | ( *) | 14 | 16 |  * |
+| (?:(?P<n1>^(?:\|x))) | 0 | 19 | (?:(?P<n1>^(?:\|x))) | 3 | 18 | (?P<n1>^(?:\|x)) |
+| (?:(?P<n1>^(?:\|x))) | 3 | 18 | (?P<n1>^(?:\|x)) | 10 | 17 | ^(?:\|x) |
+| (?:(?P<n1>^(?:\|x))) | 11 | 17 | (?:\|x) | 14 | 16 | \|x |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 0 | 10 | (?:[^%]\|^) | 3 | 9 | [^%]\|^ |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | 14 | 19 | (\\w*) | 15 | 18 | \\w* |
 | (?P<name>[\\w]+)\| | 0 | 15 | (?P<name>[\\w]+) | 9 | 14 | [\\w]+ |
diff --git a/python/ql/test/library-tests/regex/Regex.expected b/python/ql/test/library-tests/regex/Regex.expected
index 788c7c28a3e..008607eabc9 100644
--- a/python/ql/test/library-tests/regex/Regex.expected
+++ b/python/ql/test/library-tests/regex/Regex.expected
@@ -41,6 +41,16 @@
 | (?:(?:\n\r?)\|^)( *)\\S | sequence | 3 | 10 |
 | (?:(?:\n\r?)\|^)( *)\\S | sequence | 6 | 9 |
 | (?:(?:\n\r?)\|^)( *)\\S | sequence | 11 | 12 |
+| (?:(?P<n1>^(?:\|x))) | ^ | 10 | 11 |
+| (?:(?P<n1>^(?:\|x))) | char | 15 | 16 |
+| (?:(?P<n1>^(?:\|x))) | choice | 14 | 16 |
+| (?:(?P<n1>^(?:\|x))) | non-empty group | 0 | 19 |
+| (?:(?P<n1>^(?:\|x))) | non-empty group | 3 | 18 |
+| (?:(?P<n1>^(?:\|x))) | non-empty group | 11 | 17 |
+| (?:(?P<n1>^(?:\|x))) | sequence | 0 | 19 |
+| (?:(?P<n1>^(?:\|x))) | sequence | 3 | 18 |
+| (?:(?P<n1>^(?:\|x))) | sequence | 10 | 17 |
+| (?:(?P<n1>^(?:\|x))) | sequence | 15 | 16 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | ^ | 8 | 9 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | char | 5 | 6 |
 | (?:[^%]\|^)?%\\((\\w*)\\)[a-z] | char | 11 | 12 |
@@ -123,6 +133,9 @@
 | \\\|\\[\\][123]\|\\{\\} | choice | 0 | 16 |
 | \\\|\\[\\][123]\|\\{\\} | sequence | 0 | 11 |
 | \\\|\\[\\][123]\|\\{\\} | sequence | 12 | 16 |
+| \|x | char | 1 | 2 |
+| \|x | choice | 0 | 2 |
+| \|x | sequence | 1 | 2 |
 | ^(^y\|^z)(u$\|v$)$ | $ | 10 | 11 |
 | ^(^y\|^z)(u$\|v$)$ | $ | 13 | 14 |
 | ^(^y\|^z)(u$\|v$)$ | $ | 15 | 16 |
@@ -193,6 +206,9 @@
 | ax{,3} | char | 5 | 6 |
 | ax{,3} | qualified | 1 | 6 |
 | ax{,3} | sequence | 0 | 6 |
+| x\| | char | 0 | 1 |
+| x\| | choice | 0 | 2 |
+| x\| | sequence | 0 | 1 |
 | x\|(?<!\\w)l | char | 0 | 1 |
 | x\|(?<!\\w)l | char | 6 | 8 |
 | x\|(?<!\\w)l | char | 9 | 10 |
diff --git a/python/ql/test/library-tests/regex/test.py b/python/ql/test/library-tests/regex/test.py
index f883b4b147b..44b2825dcc3 100644
--- a/python/ql/test/library-tests/regex/test.py
+++ b/python/ql/test/library-tests/regex/test.py
@@ -50,3 +50,10 @@ re.compile("", re.VERBOSE|re.DOTALL)
 re.compile("", flags=re.VERBOSE|re.IGNORECASE)
 re.search("", None, re.UNICODE)
 x = re.search("", flags=re.UNICODE)
+
+#empty choice
+re.compile(r'|x')
+re.compile(r'x|')
+
+#Named group with caret and empty choice.
+re.compile(r'(?:(?P<n1>^(?:|x)))')
diff --git a/python/ql/test/query-tests/Expressions/Regex/test.py b/python/ql/test/query-tests/Expressions/Regex/test.py
index 6a5742a8613..53576557394 100644
--- a/python/ql/test/query-tests/Expressions/Regex/test.py
+++ b/python/ql/test/query-tests/Expressions/Regex/test.py
@@ -133,3 +133,6 @@ VERBOSE_REGEX = r"""
 
 # Compiled regular expression marking it as verbose
 ODASA_6786 = re.compile(VERBOSE_REGEX, re.VERBOSE)
+
+#Named group with caret and empty choice.
+re.compile(r'(?:(?P<n1>^(?:|x)))')