diff --git a/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll b/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
index 968e19d10b0..326b3e7ae15 100644
--- a/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
+++ b/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
@@ -162,7 +162,9 @@ class RegExp extends StringLiteral {
       or
       this.namedCharacterProperty(start, end, _)
       or
-      exists(this.nonEscapedCharAt(start)) and end = start + 1
+      exists(this.nonEscapedCharAt(start)) and
+      not this.inAnyPosixBracket(start) and
+      end = start + 1
     )
     or
     this.charSetToken(charsetStart, _, start) and
@@ -172,6 +174,7 @@ class RegExp extends StringLiteral {
       this.namedCharacterProperty(start, end, _)
       or
       exists(this.nonEscapedCharAt(start)) and
+      not this.inAnyPosixBracket(start) and
       end = start + 1 and
       not this.getChar(start) = "]"
     )
@@ -313,6 +316,13 @@ class RegExp extends StringLiteral {
   private predicate posixStyleNamedCharacterProperty(int start, int end, string name) {
     this.getChar(start) = "[" and
     this.getChar(start + 1) = ":" and
+    // POSIX bracket expressions are only valid nested inside another character
+    // class. Approximate this by requiring at least one more (non-escaped)
+    // opening `[` than closing `]` before `start`. A well-formed POSIX bracket
+    // contributes one `[` and one `]` at/after `start`, so this check is
+    // unaffected by other POSIX brackets earlier in the text.
+    count(int p | p < start and this.nonEscapedCharAt(p) = "[") >
+      count(int p | p < start and this.nonEscapedCharAt(p) = "]") and
     end =
       min(int e |
         e > start and
@@ -337,6 +347,8 @@ class RegExp extends StringLiteral {
   private predicate posixCollatingSymbol(int start, int end, string name) {
     this.getChar(start) = "[" and
     this.getChar(start + 1) = "." and
+    count(int p | p < start and this.nonEscapedCharAt(p) = "[") >
+      count(int p | p < start and this.nonEscapedCharAt(p) = "]") and
     end =
       min(int e |
         e > start and
@@ -355,6 +367,8 @@ class RegExp extends StringLiteral {
   private predicate posixEquivalenceClass(int start, int end, string name) {
     this.getChar(start) = "[" and
     this.getChar(start + 1) = "=" and
+    count(int p | p < start and this.nonEscapedCharAt(p) = "[") >
+      count(int p | p < start and this.nonEscapedCharAt(p) = "]") and
     end =
       min(int e |
         e > start and
diff --git a/cpp/ql/test/library-tests/regex/locations.expected b/cpp/ql/test/library-tests/regex/locations.expected
index f9fba8ee68c..a70822fa3a6 100644
--- a/cpp/ql/test/library-tests/regex/locations.expected
+++ b/cpp/ql/test/library-tests/regex/locations.expected
@@ -6,10 +6,19 @@
 | test.cpp:143:29:143:29 | p | 23 | 5 | 6 | 29 | 29 |
 | test.cpp:143:30:143:30 | h | 23 | 6 | 7 | 30 | 30 |
 | test.cpp:143:31:143:31 | a | 23 | 7 | 8 | 31 | 31 |
+| test.cpp:146:24:146:35 | []a[:alpha:] | 23 | 0 | 12 | 24 | 35 |
 | test.cpp:146:24:146:36 | []a[:alpha:]] | 23 | 0 | 13 | 24 | 36 |
 | test.cpp:146:25:146:25 | ] | 23 | 1 | 2 | 25 | 25 |
 | test.cpp:146:26:146:26 | a | 23 | 2 | 3 | 26 | 26 |
-| test.cpp:146:27:146:35 | [:alpha:] | 23 | 3 | 12 | 27 | 35 |
+| test.cpp:146:27:146:27 | [ | 23 | 3 | 4 | 27 | 27 |
+| test.cpp:146:28:146:28 | : | 23 | 4 | 5 | 28 | 28 |
+| test.cpp:146:29:146:29 | a | 23 | 5 | 6 | 29 | 29 |
+| test.cpp:146:30:146:30 | l | 23 | 6 | 7 | 30 | 30 |
+| test.cpp:146:31:146:31 | p | 23 | 7 | 8 | 31 | 31 |
+| test.cpp:146:32:146:32 | h | 23 | 8 | 9 | 32 | 32 |
+| test.cpp:146:33:146:33 | a | 23 | 9 | 10 | 33 | 33 |
+| test.cpp:146:34:146:34 | : | 23 | 10 | 11 | 34 | 34 |
+| test.cpp:146:36:146:36 | ] | 23 | 12 | 13 | 36 | 36 |
 | test.cpp:149:25:149:53 | [[:alpha:][:digit:][:space:]] | 24 | 0 | 29 | 25 | 53 |
 | test.cpp:149:26:149:34 | [:alpha:] | 24 | 1 | 10 | 26 | 34 |
 | test.cpp:149:35:149:43 | [:digit:] | 24 | 10 | 19 | 35 | 43 |
diff --git a/cpp/ql/test/library-tests/regex/parse.expected b/cpp/ql/test/library-tests/regex/parse.expected
index 47307602ac8..b1ee43d1748 100644
--- a/cpp/ql/test/library-tests/regex/parse.expected
+++ b/cpp/ql/test/library-tests/regex/parse.expected
@@ -515,26 +515,81 @@ test.cpp:
 
 #  128| [RegExpConstant, RegExpNormalChar] f
 
-#  131| [RegExpNamedCharacterProperty] [:digit:]
+#  131| [RegExpCharacterClass] [:digit:]
+#-----| 0 -> [RegExpConstant, RegExpNormalChar] :
+#-----| 1 -> [RegExpConstant, RegExpNormalChar] d
+#-----| 2 -> [RegExpConstant, RegExpNormalChar] i
+#-----| 3 -> [RegExpConstant, RegExpNormalChar] g
+#-----| 4 -> [RegExpConstant, RegExpNormalChar] i
+#-----| 5 -> [RegExpConstant, RegExpNormalChar] t
+#-----| 6 -> [RegExpConstant, RegExpNormalChar] :
 
-#  134| [RegExpNamedCharacterProperty] [:alpha:]
+#  131| [RegExpConstant, RegExpNormalChar] :
+
+#  131| [RegExpConstant, RegExpNormalChar] d
+
+#  131| [RegExpConstant, RegExpNormalChar] i
+
+#  131| [RegExpConstant, RegExpNormalChar] g
+
+#  131| [RegExpConstant, RegExpNormalChar] i
+
+#  131| [RegExpConstant, RegExpNormalChar] t
+
+#  131| [RegExpConstant, RegExpNormalChar] :
+
+#  134| [RegExpCharacterClass] [:alpha:]
+#-----| 0 -> [RegExpConstant, RegExpNormalChar] :
+#-----| 1 -> [RegExpConstant, RegExpNormalChar] a
+#-----| 2 -> [RegExpConstant, RegExpNormalChar] l
+#-----| 3 -> [RegExpConstant, RegExpNormalChar] p
+#-----| 4 -> [RegExpConstant, RegExpNormalChar] h
+#-----| 5 -> [RegExpConstant, RegExpNormalChar] a
+#-----| 6 -> [RegExpConstant, RegExpNormalChar] :
+
+#  134| [RegExpConstant, RegExpNormalChar] :
+
+#  134| [RegExpConstant, RegExpNormalChar] a
+
+#  134| [RegExpConstant, RegExpNormalChar] l
+
+#  134| [RegExpConstant, RegExpNormalChar] p
+
+#  134| [RegExpConstant, RegExpNormalChar] h
+
+#  134| [RegExpConstant, RegExpNormalChar] a
+
+#  134| [RegExpConstant, RegExpNormalChar] :
 
 #  137| [RegExpConstant, RegExpNormalChar] a
 
-#  137| [RegExpNamedCharacterProperty] [:b:]
+#  137| [RegExpSequence] a[:b:]c
+#-----| 0 -> [RegExpConstant, RegExpNormalChar] a
+#-----| 1 -> [RegExpCharacterClass] [:b:]
+#-----| 2 -> [RegExpConstant, RegExpNormalChar] c
+
+#  137| [RegExpCharacterClass] [:b:]
+#-----| 0 -> [RegExpConstant, RegExpNormalChar] :
+#-----| 1 -> [RegExpConstant, RegExpNormalChar] b
+#-----| 2 -> [RegExpConstant, RegExpNormalChar] :
+
+#  137| [RegExpConstant, RegExpNormalChar] :
+
+#  137| [RegExpConstant, RegExpNormalChar] b
+
+#  137| [RegExpConstant, RegExpNormalChar] :
 
 #  137| [RegExpConstant, RegExpNormalChar] c
 
 #  140| [RegExpCharacterClass] [[:alpha:]-z]
-#-----| 0 -> [RegExpNamedCharacterProperty] [:alpha:]
+#-----| 0 -> [RegExpCharacterRange] [:alpha:]-z
 
 #  140| [RegExpNamedCharacterProperty] [:alpha:]
 
-#  140| [RegExpCharacterRange] :]-z
+#  140| [RegExpCharacterRange] [:alpha:]-z
+#-----| 0 -> [RegExpNamedCharacterProperty] [:alpha:]
 #-----| 1 -> [RegExpConstant, RegExpNormalChar] z
 
-#  140| [RegExpConstant, RegExpNormalChar] -
-
 #  140| [RegExpConstant, RegExpNormalChar] z
 
 #  143| [RegExpCharacterClass] [[:alpha]
@@ -560,16 +615,43 @@ test.cpp:
 
 #  143| [RegExpConstant, RegExpNormalChar] a
 
-#  146| [RegExpCharacterClass] []a[:alpha:]]
+#  146| [RegExpCharacterClass] []a[:alpha:]
 #-----| 0 -> [RegExpConstant, RegExpNormalChar] ]
 #-----| 1 -> [RegExpConstant, RegExpNormalChar] a
-#-----| 2 -> [RegExpNamedCharacterProperty] [:alpha:]
+#-----| 2 -> [RegExpConstant, RegExpNormalChar] [
+#-----| 3 -> [RegExpConstant, RegExpNormalChar] :
+#-----| 4 -> [RegExpConstant, RegExpNormalChar] a
+#-----| 5 -> [RegExpConstant, RegExpNormalChar] l
+#-----| 6 -> [RegExpConstant, RegExpNormalChar] p
+#-----| 7 -> [RegExpConstant, RegExpNormalChar] h
+#-----| 8 -> [RegExpConstant, RegExpNormalChar] a
+#-----| 9 -> [RegExpConstant, RegExpNormalChar] :
+
+#  146| [RegExpSequence] []a[:alpha:]]
+#-----| 0 -> [RegExpCharacterClass] []a[:alpha:]
+#-----| 1 -> [RegExpConstant, RegExpNormalChar] ]
 
 #  146| [RegExpConstant, RegExpNormalChar] ]
 
 #  146| [RegExpConstant, RegExpNormalChar] a
 
-#  146| [RegExpNamedCharacterProperty] [:alpha:]
+#  146| [RegExpConstant, RegExpNormalChar] [
+
+#  146| [RegExpConstant, RegExpNormalChar] :
+
+#  146| [RegExpConstant, RegExpNormalChar] a
+
+#  146| [RegExpConstant, RegExpNormalChar] l
+
+#  146| [RegExpConstant, RegExpNormalChar] p
+
+#  146| [RegExpConstant, RegExpNormalChar] h
+
+#  146| [RegExpConstant, RegExpNormalChar] a
+
+#  146| [RegExpConstant, RegExpNormalChar] :
+
+#  146| [RegExpConstant, RegExpNormalChar] ]
 
 #  149| [RegExpCharacterClass] [[:alpha:][:digit:][:space:]]
 #-----| 0 -> [RegExpNamedCharacterProperty] [:alpha:]
diff --git a/cpp/ql/test/library-tests/regex/regexp.expected b/cpp/ql/test/library-tests/regex/regexp.expected
index e9a8bc0511d..cdb750c90fb 100644
--- a/cpp/ql/test/library-tests/regex/regexp.expected
+++ b/cpp/ql/test/library-tests/regex/regexp.expected
@@ -200,15 +200,32 @@ term
 | test.cpp:128:37:128:37 | a | RegExpConstant,RegExpNormalChar |
 | test.cpp:128:37:128:39 | a-f | RegExpCharacterRange |
 | test.cpp:128:39:128:39 | f | RegExpConstant,RegExpNormalChar |
-| test.cpp:131:24:131:32 | [:digit:] | RegExpNamedCharacterProperty |
-| test.cpp:134:24:134:32 | [:alpha:] | RegExpNamedCharacterProperty |
+| test.cpp:131:24:131:32 | [:digit:] | RegExpCharacterClass |
+| test.cpp:131:25:131:25 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:26:131:26 | d | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:27:131:27 | i | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:28:131:28 | g | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:29:131:29 | i | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:30:131:30 | t | RegExpConstant,RegExpNormalChar |
+| test.cpp:131:31:131:31 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:24:134:32 | [:alpha:] | RegExpCharacterClass |
+| test.cpp:134:25:134:25 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:26:134:26 | a | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:27:134:27 | l | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:28:134:28 | p | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:29:134:29 | h | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:30:134:30 | a | RegExpConstant,RegExpNormalChar |
+| test.cpp:134:31:134:31 | : | RegExpConstant,RegExpNormalChar |
 | test.cpp:137:24:137:24 | a | RegExpConstant,RegExpNormalChar |
-| test.cpp:137:25:137:29 | [:b:] | RegExpNamedCharacterProperty |
+| test.cpp:137:24:137:30 | a[:b:]c | RegExpSequence |
+| test.cpp:137:25:137:29 | [:b:] | RegExpCharacterClass |
+| test.cpp:137:26:137:26 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:137:27:137:27 | b | RegExpConstant,RegExpNormalChar |
+| test.cpp:137:28:137:28 | : | RegExpConstant,RegExpNormalChar |
 | test.cpp:137:30:137:30 | c | RegExpConstant,RegExpNormalChar |
 | test.cpp:140:24:140:36 | [[:alpha:]-z] | RegExpCharacterClass |
 | test.cpp:140:25:140:33 | [:alpha:] | RegExpNamedCharacterProperty |
-| test.cpp:140:32:140:35 | :]-z | RegExpCharacterRange |
-| test.cpp:140:34:140:34 | - | RegExpConstant,RegExpNormalChar |
+| test.cpp:140:25:140:35 | [:alpha:]-z | RegExpCharacterRange |
 | test.cpp:140:35:140:35 | z | RegExpConstant,RegExpNormalChar |
 | test.cpp:143:24:143:32 | [[:alpha] | RegExpCharacterClass |
 | test.cpp:143:25:143:25 | [ | RegExpConstant,RegExpNormalChar |
@@ -218,10 +235,19 @@ term
 | test.cpp:143:29:143:29 | p | RegExpConstant,RegExpNormalChar |
 | test.cpp:143:30:143:30 | h | RegExpConstant,RegExpNormalChar |
 | test.cpp:143:31:143:31 | a | RegExpConstant,RegExpNormalChar |
-| test.cpp:146:24:146:36 | []a[:alpha:]] | RegExpCharacterClass |
+| test.cpp:146:24:146:35 | []a[:alpha:] | RegExpCharacterClass |
+| test.cpp:146:24:146:36 | []a[:alpha:]] | RegExpSequence |
 | test.cpp:146:25:146:25 | ] | RegExpConstant,RegExpNormalChar |
 | test.cpp:146:26:146:26 | a | RegExpConstant,RegExpNormalChar |
-| test.cpp:146:27:146:35 | [:alpha:] | RegExpNamedCharacterProperty |
+| test.cpp:146:27:146:27 | [ | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:28:146:28 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:29:146:29 | a | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:30:146:30 | l | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:31:146:31 | p | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:32:146:32 | h | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:33:146:33 | a | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:34:146:34 | : | RegExpConstant,RegExpNormalChar |
+| test.cpp:146:36:146:36 | ] | RegExpConstant,RegExpNormalChar |
 | test.cpp:149:25:149:53 | [[:alpha:][:digit:][:space:]] | RegExpCharacterClass |
 | test.cpp:149:26:149:34 | [:alpha:] | RegExpNamedCharacterProperty |
 | test.cpp:149:35:149:43 | [:digit:] | RegExpNamedCharacterProperty |
@@ -377,9 +403,25 @@ regExpNormalCharValue
 | test.cpp:128:27:128:27 | F | F |
 | test.cpp:128:37:128:37 | a | a |
 | test.cpp:128:39:128:39 | f | f |
+| test.cpp:131:25:131:25 | : | : |
+| test.cpp:131:26:131:26 | d | d |
+| test.cpp:131:27:131:27 | i | i |
+| test.cpp:131:28:131:28 | g | g |
+| test.cpp:131:29:131:29 | i | i |
+| test.cpp:131:30:131:30 | t | t |
+| test.cpp:131:31:131:31 | : | : |
+| test.cpp:134:25:134:25 | : | : |
+| test.cpp:134:26:134:26 | a | a |
+| test.cpp:134:27:134:27 | l | l |
+| test.cpp:134:28:134:28 | p | p |
+| test.cpp:134:29:134:29 | h | h |
+| test.cpp:134:30:134:30 | a | a |
+| test.cpp:134:31:134:31 | : | : |
 | test.cpp:137:24:137:24 | a | a |
+| test.cpp:137:26:137:26 | : | : |
+| test.cpp:137:27:137:27 | b | b |
+| test.cpp:137:28:137:28 | : | : |
 | test.cpp:137:30:137:30 | c | c |
-| test.cpp:140:34:140:34 | - | - |
 | test.cpp:140:35:140:35 | z | z |
 | test.cpp:143:25:143:25 | [ | [ |
 | test.cpp:143:26:143:26 | : | : |
@@ -390,6 +432,15 @@ regExpNormalCharValue
 | test.cpp:143:31:143:31 | a | a |
 | test.cpp:146:25:146:25 | ] | ] |
 | test.cpp:146:26:146:26 | a | a |
+| test.cpp:146:27:146:27 | [ | [ |
+| test.cpp:146:28:146:28 | : | : |
+| test.cpp:146:29:146:29 | a | a |
+| test.cpp:146:30:146:30 | l | l |
+| test.cpp:146:31:146:31 | p | p |
+| test.cpp:146:32:146:32 | h | h |
+| test.cpp:146:33:146:33 | a | a |
+| test.cpp:146:34:146:34 | : | : |
+| test.cpp:146:36:146:36 | ] | ] |
 | test.cpp:163:21:163:26 | \\u9879 | \u9879 |
 | test.cpp:171:23:171:23 | a | a |
 | test.cpp:171:25:171:25 | b | b |