diff --git a/CHANGELOG.md b/CHANGELOG.md
index 961b5abb8..bd612e72a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,11 @@
 TBD
 ===
+The below are changes for the next release, which is to be determined.
 
 * [BUG #680](https://github.com/rust-lang/regex/issues/680):
   Fixes a bug where `[[:alnum:][:^ascii:]]` dropped `[:alnum:]` from the class.
+* [BUG #859](https://github.com/rust-lang/regex/issues/859):
+  Fixes a bug where `Hir::is_match_empty` returned `false` for `\b`.
 
 
 1.5.5 (2022-03-08)
diff --git a/regex-syntax/src/hir/mod.rs b/regex-syntax/src/hir/mod.rs
index 4969f1265..f5cf992e5 100644
--- a/regex-syntax/src/hir/mod.rs
+++ b/regex-syntax/src/hir/mod.rs
@@ -334,9 +334,13 @@ impl Hir {
         info.set_any_anchored_end(false);
         info.set_literal(false);
         info.set_alternation_literal(false);
-        // A negated word boundary matches the empty string, but a normal
-        // word boundary does not!
-        info.set_match_empty(word_boundary.is_negated());
+        // A negated word boundary matches '', so that's fine. But \b does not
+        // match \b, so why do we say it can match the empty string? Well,
+        // because, if you search for \b against 'a', it will report [0, 0) and
+        // [1, 1) as matches, and both of those matches correspond to the empty
+        // string. Thus, only *certain* empty strings match \b, which similarly
+        // applies to \B.
+        info.set_match_empty(true);
         // Negated ASCII word boundaries can match invalid UTF-8.
         if let WordBoundary::AsciiNegate = word_boundary {
             info.set_always_utf8(false);
@@ -661,8 +665,8 @@ impl Hir {
     /// Return true if and only if the empty string is part of the language
     /// matched by this regular expression.
     ///
-    /// This includes `a*`, `a?b*`, `a{0}`, `()`, `()+`, `^$`, `a|b?`, `\B`,
-    /// but not `a`, `a+` or `\b`.
+    /// This includes `a*`, `a?b*`, `a{0}`, `()`, `()+`, `^$`, `a|b?`, `\b`
+    /// and `\B`, but not `a` or `a+`.
     pub fn is_match_empty(&self) -> bool {
         self.info.is_match_empty()
     }
diff --git a/regex-syntax/src/hir/translate.rs b/regex-syntax/src/hir/translate.rs
index a7ae9bc38..56afbbed8 100644
--- a/regex-syntax/src/hir/translate.rs
+++ b/regex-syntax/src/hir/translate.rs
@@ -3139,6 +3139,9 @@ mod tests {
         assert!(t(r"\pL*").is_match_empty());
         assert!(t(r"a*|b").is_match_empty());
         assert!(t(r"b|a*").is_match_empty());
+        assert!(t(r"a|").is_match_empty());
+        assert!(t(r"|a").is_match_empty());
+        assert!(t(r"a||b").is_match_empty());
         assert!(t(r"a*a?(abcd)*").is_match_empty());
         assert!(t(r"^").is_match_empty());
         assert!(t(r"$").is_match_empty());
@@ -3148,6 +3151,8 @@ mod tests {
         assert!(t(r"\z").is_match_empty());
         assert!(t(r"\B").is_match_empty());
         assert!(t_bytes(r"(?-u)\B").is_match_empty());
+        assert!(t(r"\b").is_match_empty());
+        assert!(t(r"(?-u)\b").is_match_empty());
 
         // Negative examples.
         assert!(!t(r"a+").is_match_empty());
@@ -3157,8 +3162,6 @@ mod tests {
         assert!(!t(r"a{1,10}").is_match_empty());
         assert!(!t(r"b|a").is_match_empty());
         assert!(!t(r"a*a+(abcd)*").is_match_empty());
-        assert!(!t(r"\b").is_match_empty());
-        assert!(!t(r"(?-u)\b").is_match_empty());
     }
 
     #[test]