diff --git a/regex-syntax/src/ast/parse.rs b/regex-syntax/src/ast/parse.rs
index f5b4548b23..11ca85e10d 100644
--- a/regex-syntax/src/ast/parse.rs
+++ b/regex-syntax/src/ast/parse.rs
@@ -98,10 +98,11 @@ fn is_hex(c: char) -> bool {
 /// Returns true if the given character is a valid in a capture group name.
 ///
 /// If `first` is true, then `c` is treated as the first character in the
-/// group name (which is not allowed to be a digit).
+/// group name (which must be alphabetic or underscore).
 fn is_capture_char(c: char, first: bool) -> bool {
     c == '_'
-        || (!first && c >= '0' && c <= '9')
+        || (!first
+            && ((c >= '0' && c <= '9') || c == '.' || c == '[' || c == ']'))
         || (c >= 'a' && c <= 'z')
         || (c >= 'A' && c <= 'Z')
 }
@@ -3851,6 +3852,45 @@ bar
             }))
         );
 
+        assert_eq!(
+            parser("(?P<a_1>z)").parse(),
+            Ok(Ast::Group(ast::Group {
+                span: span(0..10),
+                kind: ast::GroupKind::CaptureName(ast::CaptureName {
+                    span: span(4..7),
+                    name: s("a_1"),
+                    index: 1,
+                }),
+                ast: Box::new(lit('z', 8)),
+            }))
+        );
+
+        assert_eq!(
+            parser("(?P<a.1>z)").parse(),
+            Ok(Ast::Group(ast::Group {
+                span: span(0..10),
+                kind: ast::GroupKind::CaptureName(ast::CaptureName {
+                    span: span(4..7),
+                    name: s("a.1"),
+                    index: 1,
+                }),
+                ast: Box::new(lit('z', 8)),
+            }))
+        );
+
+        assert_eq!(
+            parser("(?P<a[1]>z)").parse(),
+            Ok(Ast::Group(ast::Group {
+                span: span(0..11),
+                kind: ast::GroupKind::CaptureName(ast::CaptureName {
+                    span: span(4..8),
+                    name: s("a[1]"),
+                    index: 1,
+                }),
+                ast: Box::new(lit('z', 9)),
+            }))
+        );
+
         assert_eq!(
             parser("(?P<").parse().unwrap_err(),
             TestError {
diff --git a/src/lib.rs b/src/lib.rs
index 2a74bf8185..430ab7e743 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -364,7 +364,7 @@ $     the end of text (or end-of-line with multi-line mode)
 
 <pre class="rust">
 (exp)          numbered capture group (indexed by opening parenthesis)
-(?P&lt;name&gt;exp)  named (also numbered) capture group (allowed chars: [_0-9a-zA-Z])
+(?P&lt;name&gt;exp)  named (also numbered) capture group (allowed chars: [_0-9a-zA-Z.\[\]])
 (?:exp)        non-capturing group
 (?flags)       set flags within current group
 (?flags:exp)   set flags for exp (non-capturing)