diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26ec169619..809e51cfe4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,8 @@ Performance improvements:
 
 Bug fixes:
 
+* [BUG #555](https://github.com/rust-lang/regex/issues/555):
+  Fix a bug where the parser would panic on patterns like `(?m){1,1}`.
 * [BUG #557](https://github.com/rust-lang/regex/issues/557):
   Fix a bug where captures could lead to an incorrect match.
 
diff --git a/regex-syntax/src/ast/parse.rs b/regex-syntax/src/ast/parse.rs
index b73baee735..9e9900c965 100644
--- a/regex-syntax/src/ast/parse.rs
+++ b/regex-syntax/src/ast/parse.rs
@@ -1100,6 +1100,13 @@ impl<'s, P: Borrow<Parser>> ParserI<'s, P> {
                 ast::ErrorKind::RepetitionMissing,
             )),
         };
+        match ast {
+            Ast::Empty(_) | Ast::Flags(_) => return Err(self.error(
+                self.span(),
+                ast::ErrorKind::RepetitionMissing,
+            )),
+            _ => {}
+        }
         if !self.bump_and_bump_space() {
             return Err(self.error(
                 Span::new(start, self.pos()),
@@ -3124,6 +3131,18 @@ bar
                 ast: Box::new(lit('a', 0)),
             })));
 
+        assert_eq!(
+            parser(r"(?i){0}").parse().unwrap_err(),
+            TestError {
+                span: span(4..4),
+                kind: ast::ErrorKind::RepetitionMissing,
+            });
+        assert_eq!(
+            parser(r"(?m){1,1}").parse().unwrap_err(),
+            TestError {
+                span: span(4..4),
+                kind: ast::ErrorKind::RepetitionMissing,
+            });
         assert_eq!(
             parser(r"a{").parse().unwrap_err(),
             TestError {
diff --git a/tests/regression.rs b/tests/regression.rs
index af96c623c0..c3d4c7d6db 100644
--- a/tests/regression.rs
+++ b/tests/regression.rs
@@ -14,6 +14,12 @@ fn regression_many_repeat_stack_overflow() {
     assert_eq!(vec![(0, 1)], findall!(re, "a"));
 }
 
+// See: https://github.com/rust-lang/regex/issues/555
+#[test]
+fn regression_invalid_repetition_expr() {
+    assert!(regex_new!("(?m){1,1}").is_err());
+}
+
 // See: https://github.com/rust-lang/regex/issues/75
 mat!(regression_unsorted_binary_search_1, r"(?i)[a_]+", "A_", Some((0, 2)));
 mat!(regression_unsorted_binary_search_2, r"(?i)[A_]+", "a_", Some((0, 2)));